ImmunoGen, Inc. - Annual Report: 2015 (Form 10-K)

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Item 8. Financial Statements and Supplementary Data

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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Form 10-K

Commission file number 0-17999

ImmunoGen, Inc.

Securities registered pursuant to Section 12(b) of the Act:

         Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. ý Yes    o No

         Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. o Yes    ý No

         Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. ý Yes    o No

         Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§229.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). ý Yes    o No

         Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. ý

         Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definitions of "large accelerated filer," "accelerated filer," and "smaller reporting company" in Rule 12b-2 of the Exchange Act. (Check one):

         Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). o Yes    ý No

         Aggregate market value, based upon the closing sale price of the shares as reported by the NASDAQ Global Select Market, of voting stock held by non-affiliates at December 31, 2014: $526,298,576 (excludes shares held by executive officers and directors). Exclusion of shares held by any person should not be construed to indicate that such person possesses the power, direct or indirect, to direct or cause the direction of management or policies of the registrant, or that such person is controlled by or under common control with the registrant. Common Stock outstanding at August 20, 2015: 86,961,537 shares.

DOCUMENTS INCORPORATED BY REFERENCE

         Portions of the definitive Proxy Statement to be delivered to shareholders in connection with the Annual Meeting of Shareholders to be held on November 10, 2015 are incorporated by reference into Part III.

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ImmunoGen, Inc.

Form 10-K

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Item 1.    Business

        In this Annual Report on Form 10-K, ImmunoGen, Inc. (ImmunoGen, Inc., together with its subsidiaries, is referred to in this document as "we", "us", "ImmunoGen", or the "Company"), incorporates by reference certain information from parts of other documents filed with the Securities and Exchange Commission. The Securities and Exchange Commission allows us to disclose important information by referring to it in that manner. Please refer to all such information when reading this Annual Report on Form 10-K. All information is as of June 30, 2015 unless otherwise indicated. For a description of the risk factors affecting or applicable to our business, see "Risk Factors," below.

Overview

        ImmunoGen is a clinical-stage biotechnology company focused on the development of targeted anticancer therapeutics. All of our wholly owned clinical and preclinical product candidates are antibody-drug conjugates, or ADCs. An ADC is a type of medicine that uses a monoclonal antibody to deliver a therapeutic agent to targeted cells.

        We developed our ADC technology to enable the creation of highly effective, well-tolerated anticancer products. An ADC with our technology comprises an antibody that binds specifically to an antigen target found on the surface of cancer cells with one of our potent cancer-cell killing, or payload, agents attached to the antibody using one of our engineered linkers. The antibody component of an ADC serves to attach the ADC specifically to a cell with its antigen target on the surface and the payload agent serves to kill the cancer cell. We have tubulin-acting payload agents, such as DM1 and DM4, which are maytansinoids, and, more recently, we developed DNA-alkylating payload agents, such as DGN462, which we call IGNs. Our linkers are engineered to keep our cell-killing agents securely attached to the antibody while traveling through the bloodstream and then control its release and activation once inside a cancer cell. The antibody component of an ADC may serve only as a targeting vehicle or it may also have anticancer activity, depending on the antigen target and the antibody selection criteria.

        We develop our own product candidates using our ADC technology and we license to other companies limited rights to use our ADC technology with their antibodies to create products. We now have three wholly owned, clinical-stage anticancer compounds—mirvetuximab soravtansine, or IMGN853, coltuximab ravtansine, formerly SAR3419, and IMGN529—and have reported preclinical data for IMGN779, which we expect to be our next clinical-stage compound. IMGN779 is the first ADC utilizing our IGN technology. The most advanced compound with our ADC technology is Roche's marketed product, Kadcyla® (ado-trastuzumab emtansine). Eight other ADC compounds and one non-ADC, or "naked" antibody product candidate, are in clinical testing through our partnerships. Our partnership agreements entitle us to earn milestone payments with agreed-upon achievements and, for therapies successfully developed and commercialized, royalties on product sales. Our current partners are: Amgen Inc., Bayer HealthCare (a subgroup of Bayer AG), Biotest AG, Eli Lilly and Company, or Lilly, Novartis Institutes for BioMedical Research, Inc., or Novartis, the Roche Group, Sanofi and Takeda. We also have a research agreement with CytomX Therapeutics that allows each company to develop probody-drug conjugates against a specified number of antigen targets using CytomX's Probody™ antibody-masking technology with our payload agents and engineered linkers.

        We were organized as a Massachusetts corporation in 1981. Our principal offices are located at 830 Winter Street, Waltham, Massachusetts (MA) 02451, and our telephone number is 781-895-0600. We maintain a website at www.immunogen.com, where certain information about us is available. Please note that information contained on the website is not a part of this document. Our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, and any amendments to those reports are available free of charge through the "Investor Information" section of our website as soon as reasonably practicable after those materials have been electronically filed with, or furnished to,

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the Securities and Exchange Commission. We have adopted a Code of Corporate Conduct that applies to all our directors, officers and employees and a Senior Officer and Financial Personnel Code of Ethics that applies to our senior officers and financial personnel. Our Code of Corporate Conduct and Senior Officer and Financial Personnel Code of Ethics are available free of charge through the "Investors" section of our website.

Pipeline: Wholly Owned and Partner Product Candidates

        Listed in the tables below are the disclosed compounds in development through our own programs and our collaborations with other companies. All of these compounds are ADCs with the exception of isatuximab, which is a therapeutic antibody. All of these compounds are in early clinical testing (Phase 1 and/or Phase 2) with the exception of Kadcyla, which is marketed, and IMGN779, which is in preclinical testing. Additional earlier-stage compounds are in development by us and several of our partners. The results in early clinical trials may not be predictive of results obtained in subsequent clinical trials and there can be no assurance that any of our or our collaborators' product candidates will advance or will demonstrate the level of safety and efficacy necessary to obtain regulatory approval.

Compounds Wholly Owned by ImmunoGen

Collaborative Partner Compounds

Our Wholly Owned Compounds

Mirvetuximab Soravtansine

        Our product candidate mirvetuximab soravtansine, or IMGN853, is a folate receptor alpha (a), or FRa,-targeting ADC that is a potential treatment for ovarian cancer and certain other FRa-positive solid tumors. This ADC comprises a FRa-binding antibody with our potent DM4 cell-killing agent attached using one of our engineered linkers.

        After the recommended Phase 2 dose of mirvetuximab soravtansine was established in the dose-finding portion of a Phase 1 trial, an expansion cohort was opened to assess the compound as a

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single-agent treatment for patients with platinum-resistant ovarian cancer. We reported the first clinical findings from this ovarian cancer expansion cohort at the American Society of Clinical Oncology, or ASCO, annual meeting in May 2015. Mirvetuximab soravtansine was found to have notable single-agent activity in patients with FRa-positive platinum-resistant ovarian cancer and was generally well tolerated. Based on these findings, we are preparing to start a Phase 2 study in late 2015 that will assess this ADC as a single-agent treatment for patients with FRa-positive heavily pre-treated ovarian cancer. To expand the opportunity for mirvetuximab soravtansine, we are also planning to initiate a Phase 2 trial assessing the compound used in combination with other standard therapies for the treatment of ovarian cancer.

        We are also assessing mirvetuximab soravtansine in the ongoing Phase 1 trial as a single-agent treatment for relapsed/refractory FRa-positive endometrial cancer, with other FRa-positive uses being assessed preclinically.

        Mirvetuximab soravtansine has been granted orphan drug status for ovarian cancer by the U.S. Food and Drug Administration, or FDA; it has also received this designation in the EU.

IMGN529 and Coltuximab Ravtansine

        IMGN529 and coltuximab ravtansine are potential treatments for diffuse large B-cell lymphoma, or DLBCL and other B-cell malignancies.

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IMGN529 includes an ImmunoGen CD37-targeting antibody that, in preclinical testing, demonstrated anticancer activity. DM1 is attached to it using one of our engineered linkers. In a dose-finding Phase 1 clinical trial, initial evidence of anticancer activity was reported with IMGN529, particularly for patients with relapsed/refractory DLBCL.



In preclinical models, IMGN529 has demonstrated synergistic activity with the CD20-targeting antibody Rituxan® (rituximab). We are planning to start clinical testing of IMGN529 in combination with rituximab in patients with DLBCL in late 2015.

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Coltuximab ravtansine, previously called SAR3419, is a CD19-targeting ADC that is a potential new treatment for DLBCL. In Phase 2 clinical testing this ADC had encouraging single-agent activity in the treatment of relapsed/refractory DLBCL. These findings were reported at the annual meeting of ASCO in 2014 and selected for "Best of ASCO".



We plan to initiate clinical testing of coltuximab ravtansine used in a combination regimen or regimens for DLBCL in 2016.

IMGN779

        IMGN779 is a potential new treatment for acute myeloid leukemia and myelodysplastic syndrome. It comprises an ImmunoGen CD33-targeting antibody with one of our new DNA-acting payload agents, DGN462, attached using one of our engineered linkers. We intend to submit an Investigational New Drug, or IND, application for it to the FDA during the latter half of 2015.

Compounds in Development by Our Partners

        The most advanced compound with our ADC technology is Roche's marketed product, Kadcyla (ado-trastuzumab emtansine). Eight earlier-stage ADCs and one therapeutic antibody are in development through our collaborations. We have opt-in rights for co-development and co-commercialization of indatuximab ravtansine, or BT-062, jointly with Biotest in the US.

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Kadcyla (ado-trastuzumab emtansine)—Kadcyla is a HER2-targeting ADC that consists of Roche's trastuzumab antibody with our DM1 cell-killing agent attached using one of our engineered linkers. Kadcyla was granted marketing approval in February 2013 by the U.S. FDA for the

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treatment of HER2-positive metastatic breast cancer in patients who previously received Herceptin® (trastuzumab) and a taxane. It also has international approvals for this indication, including in the EU and Japan. Roche is developing Kadcyla for a number of additional HER2-positive solid tumors, including stomach cancer, early breast cancer and lung cancer.

As discussed in the Out-licenses and Collaborations section below, earlier this year we entered into a royalty purchase agreement that monetized our Kadcyla royalties.

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Indatuximab ravtansine, also referred to as BT-062—This CD138-targeting ADC was created by Biotest under a license from ImmunoGen. We have opt-in rights for co-development and co-commercialization of indatuximab ravtansine with Biotest in the U.S. The timing of our opt-in for this ADC is related to certain development events, which we expect to occur in 2016.

Encouraging findings with indatuximab ravtansine in the treatment of multiple myeloma have been reported, both with the agent used alone and as part of a combination treatment regimen, and its development for this cancer is ongoing. The target for indatuximab ravtansine also has been found to occur on several types of solid tumors, and in early 2014 this ADC began clinical testing for the treatment of triple-negative breast cancer and metastatic urinary bladder cancer.

        Promising early clinical data has been reported in both solid tumors and hematological malignancies with a number of other compounds in development by our partners:

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Anetumumab ravtansine, also referred to as BAY 94-9343—This mesothelin-targeting ADC was created by Bayer under a license from ImmunoGen. BAY 94-9343 is being assessed for the treatment of mesothelioma and of ovarian cancer in early clinical trials.



•

Isatuximab, also referred to as SAR650984—This product candidate is a CD38-targeting therapeutic, or "naked", antibody initially created by ImmunoGen and licensed to Sanofi as part of a broader research collaboration. SAR650984 has shown promising activity in early clinical testing when used alone and as part of a combination regimen to treat patients with previously treated multiple myeloma. Sanofi began Phase 2 testing of SAR650984 for multiple myeloma in mid-2014.



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AMG 595—This EGFRvIII-targeting ADC also was created by Amgen under a license from ImmunoGen. It is in Phase 1 clinical testing for the treatment of patients with glioblastoma.



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SAR566658—This CA6-targeting ADC also was initially created by ImmunoGen and licensed to Sanofi as part of a broad research collaboration. It is in Phase 1 clinical testing for the treatment of CA6-positive solid tumors, such as ovarian cancer.

        Several compounds in development by our partners have entered clinical testing and to our knowledge have not yet had clinical data reported:

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AMG 172—This CD70-targeting ADC was created by Amgen under a license from ImmunoGen. It is in Phase1 clinical testing for the treatment of patients with clear cell renal cell carcinoma.



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SAR408701—This CEACAM5-targeting ADC was initially created by ImmunoGen and licensed to Sanofi as part of a broad research collaboration. It entered Phase 1 clinical testing in 2014.



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LOP628 and PCA062—These ADCs were created by Novartis under licenses from ImmunoGen and entered Phase 1 clinical testing in 2015. LOP628 targets c-Kit-positive cancers and PCA062 targets p-cadherin-positive cancers.

        Earlier stage preclinical compounds are in development by us and several of our partners including Amgen, Novartis, Lilly, Sanofi, Takeda and CytomX.

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Incidence of Relevant Cancers

        Cancer remains a leading cause of death worldwide, and is the second leading cause of death in the U.S. The American Cancer Society, or ACS, estimates that in 2015 approximately 1.7 million new cases of cancer will be diagnosed in the U.S. and that approximately 589,000 people will die from the disease. The total number of people living with cancer significantly exceeds the number of patients diagnosed with cancer in a given year as patients can live with cancer for a year or longer. Additionally, the potential market for anticancer drugs exceeds the number of patients treated as many types of cancer typically are treated with multiple compounds at the same time and because patients often receive a number of drug regimens sequentially.

        Below is information about incidence of cancers we are seeking to treat with our wholly owned compounds. In our clinical testing, we will define treatment subgroups of patients for the cancer types referenced.

        Mirvetuximab Soravtansine—Our mirvetuximab soravtansine compound is a potential treatment for ovarian cancer and potentially other cancers that highly express its target, FRa. Based on published sources, we believe approximately 21,300 new cases of ovarian cancer will be diagnosed in the US in 2015.

        IMGN529 and Coltuximab Ravtansine—We are assessing our IMGN529 compound and our coltuximab ravtansine compound as potential treatments for a type of non-Hodgkin lymphoma, or NHL, called DLBCL. Based on ACS estimates, we believe approximately 71,850 new cases of NHL will be diagnosed in the U.S. in 2015. DLBCL is the most common type of NHL, representing approximately one out of every three cases.

        IMGN779—Our preclinical IMGN779 compound is a potential treatment for acute myeloid leukemia, or AML. Based on ACS estimates, we believe approximately 20,800 new cases of AML will be diagnosed in the U.S. in 2015.

Out-licenses and Collaborations

        We selectively license restricted access to our ADC technology to other companies to expand the utilization of our technology and to provide us with cash to fund our own product programs . These agreements typically provide the licensee with rights to use our ADC technology with its antibodies or related targeting vehicles to a defined target to develop products. The licensee is generally responsible for the development, clinical testing, manufacturing, registration and commercialization of any resulting product candidate. As part of these agreements, we are generally entitled to receive upfront fees, potential milestone payments, royalties on the sales of any resulting products and research and development funding based on activities performed at our collaborative partner's request. We are also compensated for preclinical and clinical materials that we supply to our partners.

        We only receive royalty payments from our out-licenses after a product candidate developed under the license has been approved for marketing and commercialized. Additionally, the largest milestone payments under our existing collaborations usually are on later-stage events, such as commencement of pivotal clinical trials, product approval and achievement of defined annual sales levels. Achievement of product approval requires, at a minimum, favorable completion of preclinical development and evaluation, assessment of early-stage clinical trials, advancement into pivotal Phase II and/or Phase III clinical testing, completion of this later-stage clinical testing with favorable results, and completion of

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regulatory submissions and a positive regulatory decision. Below is a table setting forth our active agreements and current status of the product candidates being developed thereunder:

Roche

        In May 2000, we granted Genentech, now a unit of Roche, an exclusive development and commercialization license to use our maytansinoid ADC technology with antibodies, such as trastuzumab, or other proteins that target HER2. In February 2013, the U.S. FDA granted marketing approval to the HER2-targeting ADC compound, Kadcyla. Roche received marketing approval for Kadcyla in Japan and in the EU in September 2013 and November 2013, respectively. It has also received marketing approval in various other countries around the world. We received a $2 million upfront payment from Roche upon execution of the agreement. We are also entitled to receive up to a total of $44 million in milestone payments, plus tiered royalties on the commercial sales of Kadcyla or any other resulting products as described below.

        The royalty term is determined on a country-by-country basis, and is initially 10 years from the date of first commercial sale of Kadcyla in the country. If, on such 10th anniversary, Kadcyla is covered by a valid claim under any patents controlled by us (excluding patents jointly owned by us and Genentech), then royalties remain payable on sales of Kadcyla in that country for an additional 2 years and no more.

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        The following two territories are used in our agreement with Genentech to determine the Kadcyla sales levels for the calculation of the applicable tiered royalty levels: (1) the U.S. and (2) the rest of the world. Royalties on sales of Kadcyla are paid quarterly based on net sales in each territory in accordance with a tiered structure calculated separately in each of the two territories as follows:

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3% of net sales up to $250 million in the calendar year;



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3.5% of net sales above $250 million and up to $400 million in the calendar year;



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4% of net sales above $400 million and up to $700 million in the calendar year; and



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5% of net sales above $700 million in the calendar year.

        Royalties will be reduced to a flat 2% of net sales in any country at any time during the royalty term in which Kadcyla is not covered by a valid claim under any patents controlled by us (excluding patents jointly owned by us and Genentech or solely owned by Genentech) in such country.

        The license agreement also provides for certain adjustments to the royalties payable to us if Genentech makes certain third party license payments in order to exploit the ADC technology components of Kadcyla, although such adjustments would in no event reduce the royalties payable for any country below the greater of 50% of the royalties otherwise payable with respect to sales of Kadcyla in such country, or 2% of net sales in such country. As of the date of this annual report on Form 10-K, we are unaware of any facts or circumstances that would give rise to such an adjustment.

        Roche may terminate this agreement for convenience at any time upon 90 days' prior written notice to us. The agreement may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, the agreement will continue in effect until the expiration of Roche's royalty obligations.

        In April 2015, Immunity Royalty Holdings, L.P. paid us $200 million to purchase our right to receive 100% of the royalty payments on commercial sales of Kadcyla arising under our development and commercialization license with Genentech, until Immunity Royalty Holdings has received aggregate Kadcyla royalties equal to $235 million or $260 million, depending on when the aggregate Kadcyla royalties received by Immunity Royalty Holdings reach a specified milestone. Once the applicable threshold is met, if ever, we will thereafter receive 85% and Immunity Royalty Holdings will receive 15% of the Kadcyla royalties for the remaining royalty term.

        In fiscal year 2014 we received two $5 million milestone payments in connection with marketing approval of Kadcyla in Japan and in the EU. Through June 30, 2015, we have received and recognized a total of $34.0 million in milestone payments under this agreement. The next potential milestone we will be entitled to receive will be a $5 million regulatory milestone for marketing approval of Kadcyla for a first extended indication as defined in the agreement.

        Roche, through its Genentech unit, also has licenses for the exclusive right to use our maytansinoid ADC technology with antibodies to four undisclosed targets, which were granted under the terms of a separate May 2000 right-to-test agreement with Genentech. For each of these licenses we received a $1 million license fee and are entitled to receive up to a total of $38 million in milestone payments and also royalties on the sales of any resulting products. We have not received any milestone payments from these agreements through June 30, 2015. Roche is responsible for the development, manufacturing, and marketing of any products resulting from these licenses. Roche no longer has the right to take additional licenses under the right-to-test agreement.

Amgen

        Under a now-expired right-to-test agreement, in September 2009, November 2009 and December 2012, Amgen took three exclusive development and commercialization licenses, for which we received

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an exercise fee of $1 million for each license taken. In May 2013, Amgen took one non-exclusive development and commercialization license, for which we received an exercise fee of $500,000. In October 2013, the non-exclusive license was amended and converted to an exclusive license, for which Amgen paid an additional $500,000 fee to us. Amgen has sublicensed its rights under this license to Oxford BioTherapeutics Ltd. We are entitled to receive up to a total of $34 million in milestone payments for each exclusive license, plus royalties on the commercial sales of any resulting products.

        In November 2011, the IND applications to the FDA for two compounds developed under the 2009 development and commercialization licenses became active, which triggered two $1 million milestone payments to us. The next potential milestone we will be entitled to receive under either of these two 2009 development and commercialization licenses will be a development milestone for the first dosing of a patient in a Phase II clinical trial, which will result in a $3 million payment being due. The next potential milestones we will be entitled to receive under the December 2012 and May 2013 development and commercialization licenses will be a $1 million development milestone for IND approval.

        Amgen may terminate each development and commercialization license for convenience upon prior notice to us. Each license may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, each license will continue in effect until the expiration of Amgen's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Amgen's royalty obligations commence with the first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in each development and commercialization license.

Sanofi

Collaboration Agreement

        In July 2003, we entered into a broad collaboration agreement with Sanofi (formerly Aventis) to discover, develop and commercialize antibody-based products. The collaboration agreement provides Sanofi with worldwide development and commercialization rights to new antibody-based products directed to targets that are included in the collaboration, including the exclusive right to use our maytansinoid ADC technology in the creation of products directed to these targets. The product candidates (targets) currently in development under the collaboration include isatuximab (CD38), SAR566658 (CA6) and SAR408701 (CEACAM5) and one earlier-stage compound that has yet to be disclosed. We are entitled to receive milestone payments potentially totaling $21.5 million, per target, plus royalties on the commercial sales of any resulting products.

        The agreement may be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, the agreement will continue in effect until the expiration of Sanofi's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Sanofi's royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in the agreement.

        The collaboration agreement also provides us an option to certain co-promotion rights in the U.S. on a product-by-product basis. The terms of the collaboration agreement allow Sanofi to terminate our co-promotion rights if there is a change in control of ImmunoGen.

        Through June 30, 2015, we have received and recognized a total of $20.5 million in milestone payments related to compounds covered under this agreement now and in the past, including a total of

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$12.5 million in milestone payments related to three product candidates previously in the collaboration that have been returned to us along with the rights to the respective targets. In fiscal 2015, Sanofi initiated a Phase II clinical trial for isatuximab and a Phase I clinical trial for SAR408701 which triggered a $3 million milestone payment and a $1 million milestone payment, respectively, to us.

        The next potential milestone the Company will be entitled to receive for each of SAR566658 and SAR408701 will be a development milestone for initiation of a Phase IIb clinical trial (as defined in the agreement), which will result in each case in a $3 million payment being due. The next potential milestone the Company will be entitled to receive with respect to isatuximab will be a development milestone for initiation of a Phase III clinical trial, which will result in a $3 million payment being due. The next potential milestone the Company will be entitled to receive for the unidentified target will be a development milestone for commencement of a Phase I clinical trial, which will result in a $1 million payment being due.

Right-to-Test Agreement

        In December 2006, we entered into a right-to-test agreement with Sanofi. The agreement provides Sanofi with the right to (a) test our maytansinoid ADC technology with Sanofi's antibodies to targets under a right-to-test, or research, license, (b) take exclusive options, with certain restrictions, to specified targets for specified option periods and (c) upon exercise of those options, take exclusive licenses to use our maytansinoid ADC technology to develop and commercialize products directed to the specified targets on terms agreed upon at the inception of the right-to-test agreement. The right-to-test agreement had a three-year original term from the activation date that was renewed by Sanofi in August 2011 for its final three-year term ending August 31, 2014 by payment of a $2 million extension fee. No additional extensions are included in this agreement, although any outstanding options will remain in effect for the remainder of their respective option terms.

        For each development and commercialization license taken, we are entitled to receive an exercise fee of $2 million and up to a total of $30 million in milestone payments, plus royalties on the commercial sales of any resulting products. In December 2013, Sanofi took its first exclusive development and commercialization license under the right-to-test agreement, for which we received an exercise fee of $2 million. The next payment we could receive would either be a $2 million development milestone payment with the initiation of a Phase I clinical trial under the first development and commercialization license taken, or a $2 million exercise fee for the execution of a second license.

        Each development and commercialization license may be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, each license will continue in effect until the expiration of Sanofi's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Sanofi's royalty obligations commence with the first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in each development and commercialization license.

Biotest

        In July 2006, we granted Biotest an exclusive development and commercialization license to our maytansinoid ADC technology for use with antibodies that target CD138. The product candidate indatuximab ravtansine is in development under this agreement. We received a $1 million upfront payment from Biotest upon execution of the agreement. We are also entitled to receive up to a total of $35.5 million in milestone payments, plus royalties on the commercial sales of any resulting products. Through June 30, 2015, we have received and recognized a total of $500,000 in milestone payments

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under this agreement. The next potential milestone we will be entitled to receive will be a development milestone for commencement of a Phase IIb clinical trial (as defined in the agreement), which will result in a $2 million payment being due.

        The agreement also provided us with the right to elect, at specific stages during the clinical evaluation of any compound created under the agreement, to participate in the U.S. development and commercialization of that compound in lieu of receiving the milestone payments not yet earned and royalties on sales in the U.S. Currently, we can exercise this right during an exercise period specified in the agreement by notice and payment to Biotest of an agreed upon opt-in fee of $15 million. Upon exercise of this right, we would share equally with Biotest the associated further costs of product development and commercialization in the U.S. along with the profit, if any, from product sales in the U.S. We would also be entitled to receive royalties, on a reduced basis, on product sales outside the U.S.

        Biotest may terminate the agreement for convenience at any time prior to our election to participate in the U.S. development and commercialization of a compound created under this agreement upon prior notice to us. The agreement may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, the agreement will continue in effect until the expiration of Biotest's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Biotest's royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in the agreement.

Bayer HealthCare

        In October 2008, we granted Bayer HealthCare an exclusive development and commercialization license to our maytansinoid ADC technology for use with antibodies or other proteins that target mesothelin. The product candidate anetumumab ravtansine is in development under this agreement. We received a $4 million upfront payment upon execution of the agreement. We are also entitled to receive, for each product developed and marketed by Bayer HealthCare under this agreement, up to a total of $170.5 million in milestone payments, plus royalties on the commercial sales of any resulting products.

        Bayer HealthCare may terminate the agreement for convenience at any time upon prior written notice to us. The agreement may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. We may also terminate the agreement upon the occurrence of specified events. Unless earlier terminated, the agreement will continue in effect until the expiration of Bayer HealthCare's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Bayer HealthCare's royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in the agreement.

        Through June 30, 2015, we have received and recognized a total of $3 million in milestone payments under this agreement. The next potential milestone we will be entitled to receive will be a development milestone for commencement of a non-pivotal Phase II clinical trial, which will result in a $4 million payment being due.

Novartis

        Novartis had the right to take six exclusive development and commercialization licenses under a right-to-test agreement established in October 2010, and took these licenses prior to the expiration of

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the agreement in October 2014. We received a $45 million upfront payment in connection with the execution of the right-to-test agreement in 2010, and for each development and commercialization license taken for a specific target, we received an exercise fee of $1 million and are entitled to receive up to a total of $199.5 million in milestone payments, plus royalties on the commercial sales of any resulting products. The initial three-year term of the right-to-test agreement was extended by Novartis in October 2013 for an additional one-year period by payment of a $5 million fee to us. We also are entitled to receive payments for research and development activities performed on behalf of Novartis. Novartis is responsible for the manufacturing, product development and marketing of any products resulting from this agreement.

        In March 2013, we and Novartis amended the right-to-test agreement so that Novartis could take a license to develop and commercialize products directed at two undisclosed, related targets, one target licensed on an exclusive basis and the other target initially licensed on a non-exclusive basis. The target licensed on a non-exclusive basis may no longer be converted to an exclusive target due to the expiration of the right-to-test agreement. We received a $3.5 million fee in connection with the execution of the amendment to the agreement. We may be required to credit this fee against future milestone payments if Novartis discontinues the development of a specified product under certain circumstances.

        In connection with the amendment, in March 2013, Novartis took the license referenced above under the right-to-test agreement, as amended, enabling it to develop and commercialize products directed at the two targets. The Company received a $1 million upfront fee with the execution of this license. Additionally, the execution of this license provides the Company the opportunity to receive milestone payments totaling $199.5 million or $238 million, depending on the composition of any resulting products.

        In October 2013 and November 2013, Novartis took its second and third exclusive licenses to single targets, and in October 2014, took three remaining exclusive licenses, each triggering a $1 million payment to the Company and the opportunity to receive milestone payments totaling $199.5 million, as outlined above, plus royalties on the commercial sales of any resulting products. In January 2015, Novartis initiated Phase I, first-in-human clinical testing of its cKit-targeting ADC product candidate, LOP628, triggering a $5 million development milestone payment to the Company. In May 2015, Novartis initiated Phase I, first-in-human clinical testing of its P-cadherin-targeting ADC product candidate, PCA062, triggering a $5 million development milestone payment to the Company. The next payment the Company could receive would be either a $7.5 million development milestone for commencement of a Phase II clinical trial under either of these two licenses or a $5 million development milestone for commencement of a Phase I clinical trial under any of its other four licenses. Additionally, the Company is entitled to receive royalties on product sales, if any.

        Novartis may terminate any development and commercialization license for convenience upon prior notice to us. Each license may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, each development and commercialization license will continue in effect until the expiration of Novartis' royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Novartis' royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in each license.

Lilly

        Lilly had the right to take three exclusive development and commercialization licenses under a right-to-test agreement established in December 2011, and took these licenses prior to the expiration of

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the agreement in December 2014. We received a $20 million upfront payment in connection with the execution of the right-to-test agreement in 2011. Under the terms of this right-to-test agreement, the first license had no associated exercise fee, and the second and third licenses each had a $2 million exercise fee. The first development and commercialization license was taken in August 2013 and the agreement was amended in December 2013 to provide Lilly with an extension provision and retrospectively include a $2 million exercise fee for the first license in lieu of the fee due for either the second or third license. The second and third licenses were taken in December 2014, with one including the $2 million exercise fee and the other not. Under the two licenses with the $2 million exercise fee, we are entitled to receive up to a total of $199 million in milestone payments, plus royalties on the commercial sales of any resulting products. Under the license taken in December 2014 without the exercise fee, the Company is entitled to receive up to a total of $200.5 million in milestone payments, plus royalties on the commercial sales of any resulting products. The next payment the Company could receive would be a $5 million development milestone payment with the initiation of a Phase I clinical trial under any of these three development and commercialization licenses taken. We also are entitled to receive payments for delivery of cytotoxic agents to Lilly and research and development activities performed on behalf of Lilly. Lilly is responsible for the manufacturing, product development and marketing of any products resulting from this collaboration.

        Lilly may terminate any development and commercialization license for convenience upon prior notice to us. Each license may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. We may also terminate the agreement upon the occurrence of specified events. Unless earlier terminated, each development and commercialization license will continue in effect until the expiration of Lilly's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Lilly's royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in each license.

CytomX

        In January 2014, we entered into a reciprocal right-to-test agreement with CytomX. The agreement provides CytomX with the right to test our ADC technology with CytomX Probodies to create Probody-drug conjugates (PDCs) directed to a specified number of targets under a right-to-test, or research, license, and to subsequently take an exclusive, worldwide license to use our ADC technology to develop and commercialize PDCs directed to the specified targets on terms agreed upon at the inception of the right-to-test agreement. We received no upfront cash payment in connection with the execution of the right-to-test agreement. Instead, we received reciprocal rights to CytomX's Probody technology whereby we were provided the right to test CytomX's Probody technology to create PDCs directed to a specified number of targets and to subsequently take exclusive, worldwide licenses to develop and commercialize PDCs directed to the specified targets on terms agreed upon at the inception of the right-to-test agreement. The terms of the right-to-test agreement require us and CytomX to each take its respective development and commercialization licenses by the end of the term of the research license. In addition, both we and CytomX are required to perform specific research activities under the right-to-test agreement on behalf of the other party for no monetary consideration.

        With respect to the development and commercialization license that may be taken by CytomX, we are entitled to receive up to a total of $160 million in milestone payments per license, plus royalties on the commercial sales of any resulting product. Assuming no annual maintenance fee is payable as described below, the next payment we could receive would be a $1 million development milestone payment with commencement of a Phase I clinical trial.

        With respect to any development and commercialization license that may be taken by us, we will potentially be required to pay up to a total of $80 million in milestone payments per license, plus

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royalties on the commercial sales of any resulting product. Assuming no annual maintenance fee is payable as described below, the next payment we could be required to make is a $1 million development milestone payment with commencement of a Phase I clinical trial.

        In addition, each party may be liable to pay annual maintenance fees to the other party if the licensed PDC product candidate covered under each development and commercialization license has not progressed to a specified stage of development within a specified time frame.

Takeda

        In March 2015, we entered into a right-to-test agreement with Takeda Pharmaceutical Company Limited (Takeda) through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. The agreement provides Takeda with the right to (a) take exclusive options, with certain restrictions, to individual targets selected by Takeda for specified option periods, (b) test our ADC technology with Takeda's antibodies directed to the targets optioned under a right-to-test, or research, license, and (c) take exclusive licenses to use our ADC technology to develop and commercialize products to targets optioned for up to two individual targets on terms specified in the right-to-test agreement. Takeda must exercise its options for the development and commercialization licenses by the end of the three-year term of the right-to-test agreement, after which any then outstanding options will lapse. Takeda has the right to extend the three-year right-to-test period for one additional year by payment to us of $4 million. Alternatively, Takeda has the right to expand the scope of the right-to-test agreement by payment to us of $8 million. If Takeda opts to expand the scope of the right-to-test agreement, it will be entitled to take additional exclusive options, one of which may be exercised for an additional development and commercialization license, and the right-to test period will be extended until the fifth anniversary of the effective date of the right-to-test agreement. Takeda is responsible for the manufacturing, product development and marketing of any products resulting from this collaboration.

        We received a $20 million upfront payment in connection with the execution of the right-to-test agreement and, for each development and commercialization license taken, are entitled to receive up to a total of $210 million in milestone payments, plus royalties on the commercial sales of any resulting products. The first potential milestone the Company will be entitled to receive will be a $5 million development milestone payment with the initiation of a Phase I clinical trial under the first development and commercialization license taken. We also are entitled to receive payments for delivery of cytotoxic agents to Takeda and research and development activities performed on behalf of Takeda.

        Takeda may terminate any development and commercialization license for convenience upon prior notice to us. Each license may also be terminated by either party for a material breach by the other, subject to notice and cure provisions. Unless earlier terminated, each development and commercialization license will continue in effect until the expiration of Takeda's royalty obligations, which are determined on a product-by-product and country-by-country basis. For each product and country, Takeda's royalty obligations commence upon first commercial sale of that product in that country, and extend until the later of either the expiration of the last-to-expire ImmunoGen patent covering that product in that country or the expiration for that country of the minimum royalty period specified in each license.

Patents, Trademarks and Trade Secrets

        Our intellectual property strategy centers on obtaining patent protection for our proprietary technologies and product candidates. As of June 30, 2015, our patent portfolio had a total of 659 issued patents worldwide and 645 pending patent applications worldwide. We seek to protect our ADC technology and our product candidates through a multi-pronged approach. In this regard, we have patents and patent applications covering antibodies and other cell-binding agents, linkers, cell-killing agents (e.g., tubulin-acting maytansinoids and DNA-acting cell-killing agents), and complete ADCs,

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comprising these components and methods of making and using each of the above. Typically, multiple issued patents and pending patent applications cover various aspects of each product candidate.

        We consider our cell-killing agent technology to be a key component of our overall corporate strategy. We currently own 50 issued U.S. patents covering various embodiments of our maytansinoid technology including claims directed to certain maytansinoids, antibody-maytansinoid conjugates and other cell-binding agents used with maytansinoids, and methods of making and using the same. In all cases, we have received or are applying for comparable patents in other jurisdictions including Europe and Japan. We have issued patents that cover numerous aspects of the manufacture of both our DM1 and DM4 cell-killing agents. These issued patents remain in force until various times between 2020 and 2026. We also have several composition of matter patents covering various aspects of our DM4 cell-killing agent and antibody-maytansinoid conjugates incorporating DM4 that are expected to remain in force until 2024-2033. We have five issued U.S. patents covering various aspects of our DNA-acting cell-killing agents, which will expire at various times between 2029 and 2033. We also have six additional pending U.S. patent applications disclosing and claiming other related embodiments of this technology. Patents that may issue from these applications will, if issued, expire between 2030 and 2036. In all cases, we are also applying for comparable patents in other jurisdictions, including Europe and Japan.

        Our intellectual property strategy also includes pursuing patents directed to linkers, antibodies, conjugation methods, ADC formulations and the use of specific antibodies and ADCs to treat certain diseases. In this regard, we have issued patents and pending patent applications related to many of our linker technologies. These issued patents, expiring in 2021-2031, and any patents which may issue from the patent applications, cover antibody-maytansinoid conjugates using these linkers. We also have issued U.S. patents and pending patent applications covering methods of assembling ADCs from their constituent antibody, linker and cell-killing agent moieties. These issued patents will expire in 2021-2030, while any patents that may issue from pending patent applications also covering various aspects of these technologies will, if issued, expire between 2021 and 2034. We also have issued patents and pending patent applications related to monoclonal antibodies that may be a component of an ADC compound or may be developed as a therapeutic, or "naked," antibody anticancer compound.

        We expect our continued work in each of these areas will lead to other patent applications. In all such cases, we will either be the assignee or owner of such patents or have an exclusive license to the technology covered by the patents.

        The rates at which we are entitled to receive royalties based on sales of Kadcyla in any particular country depend in part on whether the manufacture, use or sale of Kadcyla is covered by ImmunoGen patent rights in that country. In this regard, we own patents in the U.S. and Europe covering the composition of matter of Kadcyla that expire at the earliest in 2023 and 2024, respectively, and may be eligible for extension of those terms under applicable patent laws in those jurisdictions. We also own patents in the U.S. and Europe that cover various elements of the manufacture of Kadcyla, with expiration dates extending to at least 2027 and 2026, respectively. Notwithstanding these patent terms, the period during which we are entitled to receive royalties based on sales of Kadcyla in any country does not extend beyond the 12^th anniversary of the date of the first commercial sale of Kadcyla in such country.

        We cannot provide assurance that the patent applications will issue as patents or that any patents, if issued, will provide us with adequate protection against competitors with respect to the covered products, technologies or processes. Defining the scope and term of patent protection involves complex legal and factual analyses and, at any given time, the result of such analyses may be uncertain. In addition, other parties may challenge our patents in litigation or administrative proceedings resulting in a partial or complete loss of certain patent rights owned or controlled by ImmunoGen, Inc. Furthermore, as a patent does not confer any specific freedom to operate, other parties may have patents that may block or otherwise hinder the development and commercialization of our technology.

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        On October 29, 2014, the Patent Trial and Appeal Board of the United States Patent and Trademark Office, or PTAB, instituted an inter partes review, or IPR, of the claims in our U.S. Patent No. 8,337,856, or the '856 Patent, that covers Kadcyla. The PTAB heard oral argument in this matter on July 9, 2015, and a ruling by the PTAB is expected by the end of October 2015. The '856 Patent is one of several U.S. patents we hold that pertain to Kadcyla. Consequently, any adverse outcome of the IPR is not expected to impact either the royalty revenue we are entitled to receive from Roche on Kadcyla sales in the U.S., or the $200 million royalty monetization transaction relating to our Kadcyla royalty stream that was consummated in April 2015.

        Many of the processes and much of the know-how that are important to us depend upon the skills, knowledge and experience of our key scientific and technical personnel, which skills, knowledge and experience are not patentable. To protect our rights in these areas, we require that all employees, consultants, advisors and collaborators enter into confidentiality agreements with us. Further, we require that all employees enter into assignment of invention agreements as a condition of employment. We cannot provide assurance, however, that these agreements will provide adequate or any meaningful protection for our trade secrets, know-how or other proprietary information in the event of any unauthorized use or disclosure of such trade secrets, know-how or proprietary information. Further, in the absence of patent protection, we may be exposed to competitors who independently develop substantially equivalent technology or otherwise gain access to our trade secrets, know-how or other proprietary information.

Competition

        We focus on highly competitive areas of product development. Our competitors include major pharmaceutical companies and other biotechnology firms. For example, Pfizer, Seattle Genetics, Roche and Bristol-Myers Squibb have programs to attach a proprietary cell-killing small molecule to an antibody for targeted delivery to cancer cells. Pharmaceutical and biotechnology companies, as well as other institutions, also compete with us for promising targets for antibody-based therapeutics and in recruiting highly qualified scientific personnel. Additionally, there are non-ADC therapies available and/or in development for the cancer types we and our partners are targeting. Many competitors and potential competitors have substantially greater scientific, research and product development capabilities, as well as greater financial, marketing and human resources than we do. In addition, many specialized biotechnology firms have formed collaborations with large, established companies to support the research, development and commercialization of products that may be competitive with ours.

        In particular, competitive factors within the antibody and cancer therapeutic market include:

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the safety and efficacy of products;



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the timing of regulatory approval and commercial introduction;



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special regulatory designation of products, such as Orphan Drug designation; and



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the effectiveness of marketing, sales, and reimbursement efforts.

        Our competitive position depends on our ability to develop effective proprietary products, implement clinical development programs, production plans and marketing plans, including collaborations with other companies with greater marketing resources than ours, and to obtain patent protection and secure sufficient capital resources.

        Continuing development of conventional and targeted chemotherapeutics by large pharmaceutical companies and biotechnology companies may result in new compounds that may compete with our product candidates. Antibodies developed by certain of these companies have been approved for use as cancer therapeutics. In the future, new antibodies or other targeted therapies may compete with our product candidates. Other companies have created or have programs to create potent cell-killing agents

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for attachment to antibodies. These companies may compete with us for technology out-license arrangements.

Regulatory Matters

Government Regulation and Product Approval

        Government authorities in the U.S., at the federal, state and local level, and other countries extensively regulate, among other things, the research, development, testing, manufacture, quality control, approval, labeling, packaging, storage, record-keeping, promotion, advertising, distribution, marketing and export and import of products such as those we are developing. A new drug must be approved by the FDA through the new drug application, or NDA, process and a new biologic must be approved by the FDA through the biologics license application, or BLA, process before it may be legally marketed in the U.S.

U.S. Drug Development Process

        In the U.S., the FDA regulates drugs under the federal Food, Drug, and Cosmetic Act, or FDCA, and in the case of biologics, also under the Public Health Service Act, or PHSA, and implementing regulations. The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local, and foreign statutes and regulations require the expenditure of substantial time and financial resources. Failure to comply with the applicable U.S. requirements at any time during the product development process, approval process or after approval, may subject an applicant to administrative or judicial sanctions. These sanctions could include the FDA's refusal to approve pending applications, withdrawal of an approval, a clinical hold, warning letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, refusals of government contracts, restitution, disgorgement, or civil or criminal penalties. Any agency or judicial enforcement action could have a material adverse effect on us. The process required by the FDA before a drug or biologic may be marketed in the U.S. generally involves the following:

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completion of preclinical laboratory tests, animal studies and formulation studies according to current Good Laboratory Practices (cGLP) or other applicable regulations;



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submission to the FDA of an IND which must become effective before human clinical trials may begin;



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performance of adequate and well-controlled human clinical trials according to current Good Clinical Practices (cGCP) to establish the safety and efficacy of the proposed drug for its intended use;



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submission to the FDA of an NDA or BLA;



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satisfactory completion of an FDA inspection of the manufacturing facility or facilities at which the drug is produced to assess compliance with current Good Manufacturing Practice (cGMP) to assure that the facilities, methods and controls are adequate to preserve the drug's identity, strength, quality and purity; and



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FDA review and approval of the NDA or BLA.

        Once a pharmaceutical candidate is identified for development, it enters the preclinical testing stage. Preclinical tests include laboratory evaluations of product chemistry, toxicity and formulation, as well as animal studies. An IND sponsor must submit the results of the preclinical tests, together with manufacturing information and analytical data, to the FDA as part of the IND. The sponsor will also include a protocol detailing, among other things, the objectives of the first phase of the clinical trial, the parameters to be used in monitoring safety, and the effectiveness criteria to be evaluated, if the first phase lends itself to an efficacy evaluation. Some preclinical testing may continue even after the

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IND is submitted. The IND automatically becomes effective 30 days after receipt by the FDA, unless the FDA, within the 30-day time period, places the clinical trial on a clinical hold. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical trial can begin. Clinical holds also may be imposed by the FDA at any time before or during clinical trials due to safety concerns about on-going or proposed clinical trials or non-compliance with specific FDA requirements, and the trials may not begin or continue until the FDA notifies the sponsor that the hold has been lifted.

        All clinical trials must be conducted under the supervision of one or more qualified investigators in accordance with cGCP regulations. They must be conducted under protocols detailing the objectives of the trial, dosing procedures, subject selection and exclusion criteria and the safety and effectiveness criteria to be evaluated. Each protocol must be submitted to the FDA as part of the IND, and timely safety reports must be submitted to the FDA and the investigators for serious and unexpected adverse events. An institutional review board, or IRB, at each institution participating in the clinical trial must review and approve each protocol before a clinical trial commences at that institution and must also approve the information regarding the trial and the consent form that must be provided to each trial subject or his or her legal representative, monitor the study until completed and otherwise comply with IRB regulations.

        Human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

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Phase I:  The product candidate is initially introduced into healthy human subjects and tested for safety, dosage tolerance, absorption, metabolism, distribution and excretion. In the case of some products for severe or life-threatening diseases, such as cancer, especially when the product may be too inherently toxic to ethically administer to healthy volunteers, the initial human testing is often conducted in patients.



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Phase II:  This phase involves clinical trials in a limited patient population to identify possible adverse effects and safety risks, to preliminarily evaluate the efficacy of the product for specific targeted diseases and to determine dosage tolerance and optimal dosage.



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Phase III:  Clinical trials are undertaken to further evaluate dosage, clinical efficacy and safety in an expanded patient population at geographically dispersed clinical study sites. These clinical trials are intended to establish the overall risk-benefit ratio of the product candidate and provide, if appropriate, an adequate basis for product labeling.

        Post-approval trials, sometimes referred to as Phase IV, may be conducted after initial marketing approval. These trials are used to gain additional experience from the treatment of patients in the intended therapeutic indication. In certain instances, the FDA may mandate the performance of Phase IV clinical trials as a condition of approval of an NDA or BLA.

        The FDA or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the research subjects or patients are being exposed to an unacceptable health risk. Similarly, an IRB can suspend or terminate approval of a clinical trial at its institution if the clinical trial is not being conducted in accordance with the IRB's requirements or if the drug has been associated with unexpected serious harm to patients. Additionally, some clinical trials are overseen by an independent group of qualified experts organized by the sponsor, known as a data safety monitoring board or committee. Depending on its charter, this group may determine whether a trial may move forward at designated check points based on access to certain data from the trial. Phase I, Phase II, and Phase III testing may not be completed successfully within any specified period, if at all.

        During the development of a new drug, sponsors are given opportunities to meet with the FDA at certain points. These points may be prior to submission of an IND, at the end of Phase II, and before an NDA or BLA is submitted. Meetings at other times may be requested. These meetings can provide

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an opportunity for the sponsor to share information about the data gathered to date, for the FDA to provide advice, and for the sponsor and FDA to reach agreement on the next phase of development. Sponsors typically use the End of Phase II meeting to discuss their Phase II clinical results and present their plans for the pivotal Phase III clinical trial that they believe will support approval of the new drug. If this type of discussion occurs, a sponsor may be able to request a Special Protocol Assessment, or SPA, the purpose of which is to reach agreement with the FDA on the design of the Phase III clinical trial protocol design and analysis that will form the primary basis of an efficacy claim.

        According to FDA guidance for industry on the SPA process, a sponsor that meets the prerequisites may make a specific request for a special protocol assessment and provide information regarding the design and size of the proposed clinical trial. The FDA is required to evaluate the protocol within 45 days of the request to assess whether the proposed trial is adequate, and that evaluation may result in discussions and a request for additional information. A SPA request must be made before the proposed trial begins, and all open issues must be resolved before the trial begins. If a written agreement is reached, it will be documented and made part of the record. The agreement will be binding on the FDA and may not be changed by the sponsor or the FDA after the trial begins except with the written agreement of the sponsor and the FDA or if the FDA determines that a substantial scientific issue essential to determining the safety or efficacy of the drug was identified after the testing began. If the sponsor makes any unilateral changes to the approved protocol, the agreement will be invalidated.

        Concurrent with clinical trials, companies usually complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the drug and finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things,the manufacturer must develop methods for testing the identity, strength, quality and purity of the final drug. Additionally, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

        While the IND is active and before approval, progress reports summarizing the results of the clinical trials and nonclinical studies performed since the last progress report must be submitted at least annually to the FDA, and written IND safety reports must be submitted to the FDA and investigators for serious and unexpected suspected adverse events, findings from other studies suggesting a significant risk to humans exposed to the same or similar drugs, findings from animal or in vitro testing suggesting a significant risk to humans, and any clinically important increased incidence of a serious suspected adverse reaction compared to that listed in the protocol or investigator brochure.

        There are also requirements governing the reporting of ongoing clinical trials and completed trial results to public registries. Sponsors of certain clinical trials of FDA-regulated products are required to register and disclose specified clinical trial information, which is publicly available at www.clinicaltrials.gov. Information related to the product, patient population, phase of investigation, trial sites and investigators and other aspects of the clinical trial is then made public as part of the registration. Sponsors are also obligated to discuss the results of their clinical trials after completion. Disclosure of the results of these trials can be delayed until the new product or new indication being studied has been approved. However, there are evolving rules and increasing requirements for publication of all trial-related information, and it is possible that data and other information from trials involving drugs that never garner approval could require disclosure in the future.

U.S. Review and Approval Processes

        The results of product development, preclinical and other non-clinical studies and clinical trials, along with descriptions of the manufacturing process, analytical tests conducted on the chemistry of the

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drug, proposed labeling, and other relevant information are submitted to the FDA as part of an NDA or BLA requesting approval to market the product. The submission of an NDA or BLA is subject to the payment of user fees; a waiver of such fees may be obtained under certain limited circumstances. The FDA reviews all NDAs and BLAs submitted to ensure that they are sufficiently complete for substantive review before it accepts them for filing. The FDA may request additional information rather than accept an NDA or BLA for filing. In this event, the NDA or BLA must be resubmitted with the additional information. The resubmitted application also is subject to review before the FDA accepts it for filing. Once the submission is accepted for filing, the FDA begins an in-depth substantive review. FDA may refer the NDA or BLA to an advisory committee for review, evaluation and recommendation as to whether the application should be approved and under what conditions. The FDA is not bound by the recommendation of an advisory committee, but it generally follows such recommendations. The approval process is lengthy and often difficult, and the FDA may refuse to approve an NDA or BLA if the applicable regulatory criteria are not satisfied or may require additional clinical or other data and information. Even if such data and information is submitted, the FDA may ultimately decide that the NDA or BLA does not satisfy the criteria for approval. Data obtained from clinical trials are not always conclusive and the FDA may interpret data differently than we interpret the same data. The FDA may issue a complete response letter, which may require additional clinical or other data or impose other conditions that must be met in order to secure final approval of the NDA or BLA, or an approved letter following satisfactory completion of all aspects of the review process. The FDA reviews an NDA to determine, among other things, whether a product is safe and effective for its intended use and whether its manufacturing is cGMP-compliant to assure and preserve the product's identity, strength, quality and purity. The FDA reviews a BLA to determine, among other things whether the product is safe, pure and potent and the facility in which it is manufactured, processed, packed or held meets standards designed to assure the product's continued safety, purity and potency. Before approving an NDA or BLA, the FDA will inspect the facility or facilities where the product is manufactured.

        NDAs or BLAs receive either standard or priority review. A drug representing a significant improvement in treatment, prevention or diagnosis of disease may receive priority review. Priority review for an NDA for a new molecular entity and original BLAs will be 6 months from the date that the NDA or BLA is filed. In addition, products studied for their safety and effectiveness in treating serious or life-threatening illnesses and that provide meaningful therapeutic benefit over existing treatments may receive accelerated approval and may be approved on the basis of adequate and well-controlled clinical trials establishing that the drug product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit or on the basis of an effect on a clinical endpoint other than survival or irreversible morbidity. As a condition of approval, the FDA may require that a sponsor of a drug receiving accelerated approval perform adequate and well-controlled Phase IV clinical trials. Priority review and accelerated approval do not change the standards for approval, but may expedite the approval process.

        After the FDA evaluates an NDA or BLA, it will issue an approval letter or a Complete Response Letter. An approval letter authorizes commercial marketing of the drug with prescribing information for specific indications. A Complete Response Letter indicates that the review cycle of the application is complete and the application will not be approved in its present form. A Complete Response Letter usually describes the specific deficiencies in the NDA or BLA identified by the FDA and may require additional clinical data, such as an additional pivotal Phase III trial or other significant and time-consuming requirements related to clinical trials, nonclinical studies or manufacturing. If a Complete Response Letter is issued, the sponsor must resubmit the NDA or BLA, addressing all of the deficiencies identified in the letter, or withdraw the application. Even if such data and information are submitted, the FDA may decide that the NDA or BLA does not satisfy the criteria for approval.

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        If a product receives regulatory approval, the approval may be significantly limited to specific diseases and dosages or the indications for use may otherwise be limited, which could restrict the commercial value of the product. In addition, the FDA may require a sponsor to conduct Phase IV testing which involves clinical trials designed to further assess a drug's safety and effectiveness after NDA or BLA approval, and may require testing and surveillance programs to monitor the safety of approved products which have been commercialized. The FDA may also place other conditions on approval including the requirement for a risk evaluation and mitigation strategy, or REMS, to assure the safe use of the drug. If the FDA concludes a REMS is needed, the sponsor of the NDA must submit a proposed REMS. The FDA will not approve the NDA without an approved REMS, if required. A REMS could include medication guides, physician communication plans or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. Any of these limitations on approval or marketing could restrict the commercial promotion, distribution, prescription or dispensing of products. Marketing approval may be withdrawn for non-compliance with regulatory requirements or if problems occur following initial marketing.

        The Food and Drug Administration Safety and Innovation Act, or FDASIA, made permanent the Pediatric Research Equity Act, or PREA, which requires a sponsor to conduct pediatric clinical trials for most drugs and biologics, for a new active ingredient, new indication, new dosage form, new dosing regimen or new route of administration. Under PREA, original NDAs, BLAs and supplements thereto, must contain a pediatric assessment unless the sponsor has received a deferral or waiver. The required assessment must evaluate the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations and support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The sponsor or FDA may request a deferral of pediatric clinical trials for some or all of the pediatric subpopulations. A deferral may be granted for several reasons, including a finding that the drug or biologic is ready for approval for use in adults before pediatric clinical trials are complete or that additional safety or effectiveness data needs to be collected before the pediatric clinical trials begin. The FDA must send a non-compliance letter to any sponsor that fails to submit the required assessment, keep a deferral current or fails to submit a request for approval of a pediatric formulation.

Patent Term Restoration and Marketing Exclusivity

        Depending upon the timing, duration and specifics of FDA approval of our drugs, some of our U.S. patents may be eligible for limited patent term extension under the Drug Price Competition and Patent Term Restoration Act of 1984, referred to as the Hatch-Waxman Amendments. The Hatch-Waxman Amendments permit a patent restoration term of up to five years as compensation for patent term lost during product development and the FDA regulatory review process. However, patent term restoration cannot extend the remaining term of a patent beyond a total of 14 years from the product's approval date. The patent term restoration period is generally one-half the time between the effective date of an IND, and the submission date of an NDA or BLA, plus the time between the submission date of an NDA or BLA and the approval of that application. Only one patent applicable to an approved drug is eligible for the extension, and the extension must be applied for prior to expiration of the patent. The United States Patent and Trademark Office, in consultation with the FDA, reviews and approves the application for any patent term extension or restoration. In the future, we intend to apply for restorations of patent term for some of our currently owned or licensed patents to add patent life beyond their current expiration date, depending on the expected length of clinical trials and other factors involved in the filing of the relevant NDA.

        Pediatric exclusivity is a type of marketing exclusivity available in the U.S. The FDASIA made permanent the Best Pharmaceuticals for Children Act, or BPCA, which provides for an additional six months of marketing exclusivity if a sponsor conducts clinical trials in children in response to a written request from the FDA, or a Written Request. If the Written Request does not include clinical trials in

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neonates, the FDA is required to include its rationale for not requesting those clinical trials. The FDA may request studies on approved or unapproved indications in separate Written Requests. The issuance of a Written Request does not require the sponsor to undertake the described clinical trials. To date, we have not received any Written Requests.

Biologics Price Competition and Innovation Act of 2009

        On March 23, 2010, President Obama signed into law the Patient Protection and Affordable Care Act which included the Biologics Price Competition and Innovation Act of 2009, or BPCIA. The BPCIA amended the PHSA to create an abbreviated approval pathway for two types of "generic" biologics—biosimilars and interchangeable biologic products, and provides for a twelve-year data exclusivity period for the first approved biological product, or reference product, against which a biosimilar or interchangeable application is evaluated; however if pediatric clinical trials are performed and accepted by the FDA, the twelve-year data exclusivity period will be extended for an additional six months. A biosimilar product is defined as one that is highly similar to a reference product notwithstanding minor differences in clinically inactive components and for which there are no clinically meaningful differences between the biological product and the reference product in terms of the safety, purity and potency of the product. An interchangeable product is a biosimilar product that may be substituted for the reference product without the intervention of the health care provider who prescribed the reference product.

        The biosimilar applicant must demonstrate that the product is biosimilar based on data from (1) analytical studies showing that the biosimilar product is highly similar to the reference product; (2) animal studies (including toxicity); and (3) one or more clinical trials to demonstrate safety, purity and potency in one or more appropriate conditions of use for which the reference product is approved. In addition, the applicant must show that the biosimilar and reference products have the same mechanism of action for the conditions of use on the label, route of administration, dosage and strength, and the production facility must meet standards designed to assure product safety, purity and potency.

        An application for a biosimilar product may not be submitted until four years after the date on which the reference product was first approved. The first approved interchangeable biologic product will be granted an exclusivity period of up to one year after it is first commercially marketed, but the exclusivity period may be shortened under certain circumstances.

        The FDA has issued a number of final and draft guidances in order to implement the law. On April 28, 2015, the FDA issued the following three final guidances: "Scientific Considerations in Demonstrating Biosimilarity to a Reference Product," "Quality Considerations in Demonstrating Biosimilarity of a Therapeutic Protein Product to a Reference Product," and "Biosimilars: Questions and Answers Regarding Implementation of the Biologics Price Competition and Innovation Act of 2009 Guidance for Industry." The draft guidances include "Formal Meetings between the FDA and Biosimilar Biological Product Sponsors or Applicants" issued March 29, 2013, "Clinical Pharmacology Data to Support a Demonstration of Biosimilarity to a Reference Product" issued May 14, 2014, "Reference Product Exclusivity for Biological Products Filed Under Section 351(a) of the PHS Act" issued August 4, 2014, and "Biosimilars: Additional Questions and Answers Regarding Implementation of the Price Competition and Innovation Act of 2009," issued May 12, 2015.

        The guidance documents provide FDA's current thinking on approaches to demonstrating that a proposed biological product is biosimilar to a reference product. The FDA intends to issue additional guidance documents in the future, and has identified considerations in demonstrating interchangeability to a reference product, labeling and nonproprietary naming as several of the issues that it hopes to address in calendar year 2015. Nonetheless, the absence of final guidance documents covering all

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biosimilars issues does not prevent a sponsor from seeking licensure of a biosimilar under the BPCIA, and the FDA recently approved the first biosimilar application in the U.S.

Orphan Drug Designation

        Under the Orphan Drug Act, the FDA may grant orphan drug designation to a drug intended to treat a rare disease or condition, which is generally a disease or condition that affects fewer than 200,000 individuals in the U.S., or more than 200,000 individuals in the U.S. and for which there is no reasonable expectation that the cost of developing and making available in the U.S. a drug for this type of disease or condition will be recovered from sales in the U.S. for that drug. Orphan drug designation must be requested before submitting an NDA or BLA. After the FDA grants orphan drug designation, the identity of the therapeutic agent and its potential orphan use will be disclosed publicly by the FDA; the posting will also indicate whether a drug is no longer designated as an orphan drug. More than one product candidate may receive an orphan drug designation for the same indication. Orphan drug designation does not convey any advantage in or shorten the duration of the regulatory review and approval process.

        If a product that has orphan drug designation subsequently receives the first FDA approval for the disease for which it has such designation, the product is entitled to seven years of orphan product exclusivity, except in very limited circumstances. The FDA issued a final rule, effective August 12, 2013, intended to clarify several regulatory provisions, among which was a clarification of some of those limited circumstances. One of the provisions makes clear that the FDA will not recognize orphan drug exclusive approval if a sponsor fails to demonstrate upon approval that the drug is clinically superior to a previously approved drug, regardless of whether or not the approved drug was designated an orphan drug or had orphan drug exclusivity. Thus orphan drug exclusivity also could block the approval of one of our products for seven years if a competitor obtains approval of the same drug as defined by the FDA and we are not able to show the clinical superiority of our drug or if our product candidate is determined to be contained within the competitor's product for the same indication or disease.

        The FDA and the European Union granted Orphan Drug designation to mirvetuximab soravtansine, or IMGN853, when used for the treatment of ovarian cancer. Orphan drug designation provides us with seven years of market exclusivity that begins once mirvetuximab soravtansine receives FDA marketing approval for the use for which the orphan drug status was granted. Orphan medicinal product designation provides ImmunoGen with ten years of market exclusivity that begins once mirvetuximab soravtansine receives European approval for the use for which it was granted. We may pursue these designations for other indications for other product candidates intended for qualifying patient populations.

Expedited Review and Approval

        The FDA has various programs, including Fast Track, priority review, and accelerated approval, which are intended to expedite or simplify the process for reviewing drugs, and/or provide for approval on the basis of surrogate endpoints. Even if a drug qualifies for one or more of these programs, the FDA may later decide that the drug no longer meets the conditions for qualification or that the time period for FDA review or approval will not be shortened. Generally, drugs that may be eligible for these programs are those for serious or life-threatening conditions, those with the potential to address unmet medical needs, and those that offer meaningful benefits over existing treatments. For example, Fast Track is a process designed to facilitate the development, and expedite the review, of drugs to treat serious diseases and fill an unmet medical need. The request may be made at the time of IND submission and generally no later than the pre-BLA or pre-NDA meeting. The FDA will respond within 60 calendar days of receipt of the request. Priority review, which is requested at the time of BLA or NDA submission, is designed to give drugs that offer major advances in treatment or provide a treatment where no adequate therapy exists an initial review within six months as compared to a

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standard review time of ten months. Although Fast Track and priority review do not affect the standards for approval, the FDA will attempt to facilitate early and frequent meetings with a sponsor of a Fast Track designated drug and expedite review of the application for a drug designated for priority review. Accelerated approval provides an earlier approval of drugs to treat serious diseases, and that fill an unmet medical need based on a surrogate endpoint, which is a laboratory measurement or physical sign used as an indirect or substitute measurement representing a clinically meaningful outcome. Discussions with the FDA about the feasibility of an accelerated approval typically begin early in the development of the drug in order to identify, among other things, an appropriate endpoint. As a condition of approval, the FDA may require that a sponsor of a drug receiving accelerated approval perform post-marketing clinical trials to confirm the appropriateness of the surrogate marker trial.

        In FDASIA, Congress encouraged the FDA to utilize innovative and flexible approaches to the assessment of products under accelerated approval. The law required the FDA to issue related draft guidance within a year after the law's enactment and also promulgate confirming regulatory changes. The FDA published a final guidance on May 30, 2014, entitled "Expedited Programs for Serious Conditions—Drugs and Biologics." One of the expedited programs added by FDASIA is that for Breakthrough Therapy. A Breakthrough Therapy designation is designed to expedite the development and review of drugs that are intended to treat a serious condition where preliminary clinical evidence indicates that the drug may demonstrate substantial improvement over available therapy on a clinically significant endpoint(s). A sponsor may request Breakthrough Therapy designation at the time that the IND is submitted, or no later than at the end-of-Phase II meeting. The FDA will respond to a Breakthrough Therapy designation request within sixty days of receipt of the request. A drug that receives Breakthrough Therapy designation is eligible for all fast track designation features, intensive guidance on an efficient drug development program, beginning as early as Phase I and commitment from the FDA involving senior managers. FDA has already granted this designation to at least 60 new drugs and seven to date have received approval.

Post-Approval Requirements

        Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product may result in restrictions on the product or even complete withdrawal of the product from the market. After approval, some types of changes to the approved product, such as adding new indications, certain manufacturing changes and additional labeling claims, are subject to further FDA review and approval. Drug manufacturers and other entities involved in the manufacture and distribution of approved drugs are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMP and other laws and regulations. We rely, and expect to continue to rely, on third parties for the production of clinical and commercial quantities of our products. Future inspections by the FDA and other regulatory agencies may identify compliance issues at the facilities of our contract manufacturers that may disrupt production or distribution, or require substantial resources to correct.

        Any drug products manufactured or distributed by us or our partners pursuant to FDA approvals are subject to continuing regulation by the FDA, including, among other things, record-keeping requirements, reporting of adverse experiences with the drug, providing the FDA with updated safety and efficacy information, drug sampling and distribution requirements, complying with certain electronic records and signature requirements, and complying with FDA promotion and advertising requirements. FDA strictly regulates labeling, advertising, promotion and other types of information on products that are placed on the market. Drugs may be promoted only for the approved indications and in accordance with the provisions of the approved label.

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        From time to time, legislation is drafted, introduced and passed in Congress that could significantly change the statutory provisions governing the approval, manufacturing and marketing of products regulated by the FDA. It is impossible to predict whether further legislative changes will be enacted, or FDA regulations, guidance or interpretations changed or what the impact of such changes, if any, may be.

Foreign Regulation

        In addition to regulations in the U.S., we will be subject to a variety of foreign regulations governing clinical trials and commercial sales and distribution of our products. Whether or not we obtain FDA approval for a product, we must obtain approval by the comparable regulatory authorities of foreign countries or economic areas, such as the European Union, before we may commence clinical trials or market products in those countries or areas. The approval process and requirements governing the conduct of clinical trials, product licensing, pricing and reimbursement vary greatly from place to place, and the time may be longer or shorter than that required for FDA approval.

        Under European Union regulatory systems, a company may submit marketing authorization applications either under a centralized or decentralized procedure. The centralized procedure, which is compulsory for medicinal products produced by biotechnology or those medicinal products containing new active substances for specific indications such as the treatment of AIDS, cancer, neurodegenerative disorders, diabetes, viral diseases and designated orphan medicines, and optional for other medicines which are highly innovative. Under the centralized procedure, a marketing application is submitted to the European Medicines Agency where it will be evaluated by the Committee for Medicinal Products for Human Use and a favorable opinion typically results in the grant by the European Commission of a single marketing authorization that is valid for all European Union member states within 67 days of receipt of the opinion. The initial marketing authorization is valid for five years, but once renewed is usually valid for an unlimited period. The decentralized procedure provides for approval by one or more "concerned" member states based on an assessment of an application performed by one member state, known as the "reference" member state. Under the decentralized approval procedure, an applicant submits an application, or dossier, and related materials to the reference member state and concerned member states. The reference member state prepares a draft assessment and drafts of the related materials within 120 days after receipt of a valid application. Within 90 days of receiving the reference member state's assessment report, each concerned member state must decide whether to approve the assessment report and related materials. If a member state does not recognize the marketing authorization, the disputed points are eventually referred to the European Commission, whose decision is binding on all member states.

        As in the U.S., we may apply for designation of a product as an orphan drug for the treatment of a specific indication in the European Union before the application for marketing authorization is made. Orphan drugs in Europe enjoy economic and marketing benefits, including up to 10 years of market exclusivity for the approved indication unless another applicant can show that its product is safer, more effective or otherwise clinically superior to the orphan-designated product.

Reimbursement

        Sales of pharmaceutical products depend in significant part on the availability of third-party reimbursement. Third-party payors include government healthcare programs such as Medicare, managed care providers, private health insurers and other organizations. We anticipate third-party payors will provide reimbursement for our products. However, these third-party payors are increasingly challenging the price and examining the cost-effectiveness of medical products and services. In addition, significant uncertainty exists as to the reimbursement status of newly approved healthcare products. We may need to conduct expensive pharmacoeconomic studies in order to demonstrate the cost-effectiveness of our products. Our product candidates may not be considered cost-effective. It is

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time consuming and expensive for us to seek reimbursement from third-party payors. Reimbursement may not be available or sufficient to allow us to sell our products on a competitive and profitable basis.

        Medicare is a federal healthcare program administered by the federal government that covers individuals age 65 and over as well as individuals with certain disabilities. Drugs may be covered under one or more sections of Medicare depending on the nature of the drug and the conditions associated with and site of administration. For example, under Part D, Medicare beneficiaries may enroll in prescription drug plans offered by private entities which provide coverage for outpatient prescription drugs. Part D plans include both stand-alone prescription drug benefit plans and prescription drug coverage as a supplement to Medicare Advantage plans. Unlike Medicare Part A and B, Part D coverage is not standardized. Part D prescription drug plan sponsors are not required to pay for all covered Part D drugs, and each drug plan can develop its own drug formulary that identifies which drugs it will cover and at what tier or level.

        Medicare Part B covers most injectable drugs given in an in-patient setting and some drugs administered by a licensed medical provider in hospital outpatient departments and doctors' offices. Medicare Part B is administered by Medicare Administrative Contractors, which generally have the responsibility of making coverage decisions. Subject to certain payment adjustments and limits, Medicare generally pays for a Part B covered drug based on a percentage of manufacturer-reported average sales price which is regularly updated. We believe that most of our drugs, when approved, will be subject to the Medicare Part B rules.

        The American Recovery and Reinvestment Act of 2009 provides funding for the federal government to compare the effectiveness of different treatments for the same illness. A plan for this research will be developed by the Department of Health and Human Services, the Agency for Healthcare Research and Quality and the National Institutes for Health, and periodic reports on the status of the research and related expenditures will be made to Congress. Although the results of the comparative effectiveness studies are not intended to mandate coverage policies for public or private payors, it is not clear what effect, if any, the research will have on the sales of our product candidates, if any such product or the condition that it is intended to treat is the subject of a study. It is also possible that comparative effectiveness research demonstrating benefits in a competitor's product could adversely affect the sales of our product candidates. If third-party payors do not consider our products to be cost- effective compared to other available therapies, they may not cover our products after approval as a benefit under their plans or, if they do, the level of payment may not be sufficient to allow us to sell our products on a profitable basis.

        We expect that there will continue to be a number of federal and state proposals to implement governmental pricing controls and limit the growth of healthcare costs, including the cost of prescription drugs. For example, the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Affordability Reconciliation Act of 2010 (collectively, ACA) enacted in March 2010, was expected to have a significant impact on the health care industry. ACA has resulted in expanded coverage for the uninsured and is expected to help contain overall healthcare costs. With regard to pharmaceutical products, among other things, ACA is expected to expand and increase industry rebates for drugs covered under Medicaid programs and make changes to the coverage requirements under the Medicare Part D program. We cannot predict the impact of ACA on pharmaceutical companies as many of the ACA reforms require the promulgation of detailed regulations implementing the statutory provisions which has not yet occurred. In addition, although the United States Supreme Court upheld the constitutionality of most of the ACA, some states have stated their intentions to not implement certain sections of ACA and some members of Congress are still working to repeal ACA. These challenges add to the uncertainty of the changes enacted as part of ACA.

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        In addition, in some foreign countries, the proposed pricing for a drug must be approved before it may be lawfully marketed. The requirements governing drug pricing vary widely from country to country. For example, the European Union provides options for its member states to restrict the range of medicinal products for which their national health insurance systems provide reimbursement and to control the prices of medicinal products for human use. A member state may approve a specific price for the medicinal product or it may instead adopt a system of direct or indirect controls on the profitability of the company placing the medicinal product on the market. There can be no assurance that any country that has price controls or reimbursement limitations for pharmaceutical products will allow favorable reimbursement and pricing arrangements for any of our products. Historically, products launched in the European Union do not follow price structures of the U.S. and generally tend to be significantly lower.

Research and Development Spending

        During each of the three years ended June 30, 2015, 2014 and 2013, we spent approximately $111.8 million, $107.0 million and $87.1 million, respectively, on research and development activities.

Raw Materials and Manufacturing

        We procure certain raw material components of finished conjugate, including antibodies, cytotoxic agents, and linker, for ourselves and on behalf of our collaborators. In order to meet our commitments to our collaborators as well as our own needs, we are required to enter into agreements with third parties to produce these components well in advance of our production needs. Our principal suppliers for these components include Boehringer Ingelheim, BSP Pharmaceuticals S.r.l., SAFC, Inc., Carbogen Amcis and Società Italiana Corticosteroidi S.r.l.

        In addition, we operate a conjugate manufacturing facility. A portion of the cost of operating this facility, including the cost of manufacturing personnel, is incurred to conjugate material on behalf of our collaborators for which we receive payments based on the number of batches of preclinical and clinical materials produced on their behalf. Over the past few years, we have expanded and upgraded the capabilities of our manufacturing facility.

Employees

        As of June 30, 2015, we had 317 full-time employees, of whom 272 were engaged in research and development activities. Of the 272 research and development employees, 134 employees hold post- graduate degrees, of which 61 hold Ph.D. degrees and six hold M.D. degrees. We consider our relations with our employees to be good. None of our employees is covered by a collective bargaining agreement.

        We have entered into confidentiality agreements with all of our employees, members of our board of directors and consultants. Further, we have entered into assignment of invention agreements with all of our employees.

Third-Party Trademarks

        Herceptin and Kadcyla are registered trademarks of Genentech. Rituxan is a registered trademark of Biogen Inc. Probody is a trademark of CytomX Therapeutics, Inc.

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Item 1A.    Risk Factors

THE RISKS AND UNCERTAINTIES DESCRIBED BELOW ARE THOSE THAT WE CURRENTLY BELIEVE MAY MATERIALLY AFFECT OUR COMPANY. ADDITIONAL RISKS AND UNCERTAINTIES THAT WE ARE UNAWARE OF OR THAT WE CURRENTLY DEEM IMMATERIAL ALSO MAY BECOME IMPORTANT FACTORS THAT AFFECT OUR COMPANY.

We have a history of operating losses and expect to incur significant additional operating losses.

        We have generated operating losses since our inception. As of June 30, 2015, we had an accumulated deficit of $708.9 million. For the years ended June 30, 2015, 2014, and 2013, we generated losses of $60.7 million, $71.4 million and $72.8 million, respectively. We may never be profitable. We expect to incur substantial additional operating expenses over the next several years as our research, development, preclinical testing, clinical trials and collaborator support activities continue. We intend to continue to invest significantly in our product candidates. Further, we expect to invest some of our resources to support our existing collaborators as they work to develop, test and commercialize ADC compounds. We or our collaborators may encounter technological or regulatory difficulties as part of this development and commercialization process that we cannot overcome or remedy. We may also incur substantial marketing and other costs in the future if we decide to establish marketing and sales capabilities to commercialize our product candidates. Our revenues to date have been primarily from upfront and milestone payments, research and development support and clinical materials reimbursement from our collaborative partners and increasingly from royalties received from the commercial sales of Kadcyla. We do not expect to generate revenues from the commercial sale of our internal product candidates in the near future, and we may never generate revenues from the commercial sale of internal products. Even if we do successfully develop products that can be marketed and sold commercially, we will need to generate significant revenues from those products to achieve and maintain profitability. Even if we do become profitable, we may not be able to sustain or increase profitability on a quarterly or annual basis.

If we are unable to obtain additional funding when needed, we may have to delay or scale back some of our programs or grant rights to third parties to develop and market our product candidates.

        We will continue to expend substantial resources developing new and existing product candidates, including costs associated with research and development, acquiring new technologies, conducting preclinical studies and clinical trials, obtaining regulatory approvals and manufacturing products as well as providing certain support to our collaborators in the development of their products. We believe that our current working capital and expected future payments from our existing collaboration arrangements will be sufficient to meet our current and projected operating and capital requirements through fiscal 2017. However, we cannot provide assurance that such collaborative agreement funding will, in fact, be received. Should such future collaborator payments not be earned and paid as currently anticipated, we expect we could seek additional funding from other sources. We may need additional financing sooner due to a number of other factors as well, including:

•

if either we incur higher than expected costs or we or any of our collaborators experience slower than expected progress in developing product candidates and obtaining regulatory approvals;



•

acquisition of technologies and other business opportunities that require financial commitments.

        Additional funding may not be available to us on favorable terms, or at all. We may raise additional funds through public or private financings, collaborative arrangements or other arrangements. Debt financing, if available, may involve covenants that could restrict our business activities. If we are unable to raise additional funds through equity or debt financing when needed, we may be required to delay, scale back or eliminate expenditures for some of our development programs or grant rights to develop and market product candidates that we would otherwise prefer to internally

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develop and market. If we are required to grant such rights, the ultimate value of these product candidates to us may be reduced.

If our ADC technology does not produce safe, effective and commercially viable products, our business will be severely harmed.

        Our ADC technology yields novel product candidates for the treatment of cancer. To date, only one ADC using our technology, Kadcyla, has obtained marketing approval. Our ADC product candidates and/or our collaborators' ADC product candidates may not prove to be safe, effective or commercially viable treatments for cancer and our ADC technology may not result in any future meaningful benefits to us or for our current or potential collaborative partners. Furthermore, we are aware of only two other compounds that are a conjugate of an antibody and a cytotoxic small molecule that have obtained marketing approval by the FDA and are based on technology similar to our ADC technology. One of these products was later taken off the market by its owner due to toxicity concerns. If our ADC technology fails to generate product candidates that are safe, effective and commercially viable treatments for cancer or such product candidates fail to obtain FDA approval, our business will be severely harmed.

Clinical trials for our and our collaborative partners' product candidates will be lengthy and expensive and their outcome is uncertain.

        Before obtaining regulatory approval for the commercial sale of any product candidates, we and our collaborative partners must demonstrate through clinical testing that our product candidates are safe and effective for use in humans. Conducting clinical trials is a time-consuming, expensive and uncertain process and typically requires years to complete. In our industry, the results from preclinical studies and early clinical trials often are not predictive of results obtained in later-stage clinical trials. Some compounds that have shown promising results in preclinical studies or early clinical trials subsequently fail to establish sufficient safety and efficacy data necessary to obtain regulatory approval. At any time during the clinical trials, we, our collaborative partners, or the FDA might delay or halt any clinical trials of our product candidates for various reasons, including:

•

occurrence of unacceptable toxicities or side effects;



•

ineffectiveness of the product candidate;



•

insufficient drug supply;



•

negative or inconclusive results from the clinical trials, or results that necessitate additional studies or clinical trials;



•

delays in obtaining or maintaining required approvals from institutions, review boards or other reviewing entities at clinical sites;



•

delays in patient enrollment;



•

insufficient funding or a reprioritization of financial or other resources; or



•

other reasons that are internal to the businesses of our collaborative partners, which they may not share with us.

        Any failure or substantial delay in successfully completing clinical trials and obtaining regulatory approval for our product candidates or our collaborative partners' product candidates could severely harm our business.

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We and our collaborative partners are subject to extensive government regulations and we and our collaborative partners may not be able to obtain necessary regulatory approvals.

        We and our collaborative partners may not receive the regulatory approvals necessary to commercialize our product candidates, which would cause our business to be severely harmed. Pharmaceutical product candidates, including those in development by us and our collaborative partners, are subject to extensive and rigorous government regulation. The FDA regulates, among other things, the development, testing, manufacture, safety, record-keeping, labeling, storage, approval, advertising, promotion, sale and distribution of pharmaceutical products. If our potential products or our collaborators' potential products are marketed abroad, they will also be subject to extensive regulation by foreign governments. The regulatory review and approval process, which includes preclinical studies and clinical trials of each product candidate, is lengthy, complex, expensive and uncertain. Securing FDA approval requires the submission of extensive preclinical and clinical data and supporting information to the FDA for each indication to establish the product candidate's safety and efficacy. Data obtained from preclinical studies and clinical trials are susceptible to varying interpretation, which may delay, limit or prevent regulatory approval. The approval process may take many years to complete and may involve ongoing requirements for post-marketing studies. Any FDA or other regulatory approvals of our or our collaborative partners' product candidates, once obtained, may be withdrawn. The effect of government regulation may be to:

•

delay marketing of potential products for a considerable period of time;



•

limit the indicated uses for which potential products may be marketed;



•

impose costly requirements on our activities; and



•

place us at a competitive disadvantage to other pharmaceutical and biotechnology companies.

        We may encounter delays or rejections in the regulatory approval process because of additional government regulation from future legislation or administrative action or changes in FDA policy during the period of product development, clinical trials and FDA regulatory review. Failure to comply with FDA or other applicable regulatory requirements may result in criminal prosecution, civil penalties, recall or seizure of products, total or partial suspension of production or injunction, as well as other regulatory action against our product candidates or us. Outside the U.S., our ability to market a product is contingent upon receiving clearances from the appropriate regulatory authorities. The foreign regulatory approval process includes similar risks to those associated with the FDA approval process. In addition, we are, or may become, subject to various federal, state and local laws, regulations and recommendations relating to safe working conditions, laboratory and manufacturing practices, the experimental use of animals and the use and disposal of hazardous substances, including radioactive compounds and infectious disease agents, used in connection with our research work. If we fail to comply with the laws and regulations pertaining to our business, we may be subject to sanctions, including the temporary or permanent suspension of operations, product recalls, marketing restrictions and civil and criminal penalties.

Our and our collaborative partners' product candidates will remain subject to ongoing regulatory review even if they receive marketing approval. If we or our collaborative partners fail to comply with continuing regulations, these approvals could be lost and the sale of our or our collaborative partners' products could be suspended.

        Even if we or our collaborative partners receive regulatory approval to market a particular product candidate, the approval could be conditioned on us or our collaborative partners conducting costly post-approval studies or could limit the indicated uses included in product labeling. Moreover, the product may later cause adverse effects that limit or prevent its widespread use, force us or our collaborative partners to withdraw it from the market or impede or delay our or our collaborative

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partners' ability to obtain regulatory approvals in additional countries. In addition, the manufacturer of the product and its facilities will continue to be subject to FDA review and periodic inspections to ensure adherence to applicable regulations. After receiving marketing approval, the manufacturing, labeling, packaging, adverse event reporting, storage, advertising, promotion and record-keeping related to the product remain subject to extensive regulatory requirements. We or our collaborative partners may be slow to adapt, or we or our collaborative partners may never adapt, to changes in existing regulatory requirements or adoption of new regulatory requirements.

        If we or our collaborative partners fail to comply with the regulatory requirements of the FDA and other applicable U.S. and foreign regulatory authorities, or if previously unknown problems with our or our partners' products, manufacturers or manufacturing processes are discovered, we could be subject to administrative or judicially imposed sanctions, including:

•

restrictions on the products, manufacturers or manufacturing processes;



•

warning letters;



•

civil or criminal penalties;



•

fines;



•

injunctions;



•

product seizures or detentions;



•

import bans;



•

voluntary or mandatory product recalls and publicity requirements;



•

suspension or withdrawal of regulatory approvals;



•

total or partial suspension of production; and



•

refusal to approve pending applications for marketing approval of new drugs or supplements to approved applications.

        Any one of these could have a material adverse effect on our business or financial condition.

If our collaborative partners fail to perform their obligations under our agreements with them, or determine not to continue with clinical trials for particular product candidates, our business could be severely impacted.

        Our strategy for the development and commercialization of our product candidates depends, in large part, upon the formation and maintenance of collaborative arrangements. Collaborations provide an opportunity for us to:

•

generate cash flow and revenue;



•

fund some of the costs associated with our internal research and development, preclinical testing, clinical trials and manufacturing;



•

seek and obtain regulatory approvals faster than we could on our own;



•

successfully commercialize existing and future product candidates; and



•

secure access to targets which, due to intellectual property restrictions, would otherwise be unavailable to our technology.

        If we fail to secure or maintain successful collaborative arrangements, the development and marketing of compounds that use our technology may be delayed, scaled back or otherwise may not occur. In addition, we may be unable to negotiate other collaborative arrangements or, if necessary,

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modify our existing arrangements on acceptable terms. We cannot control the amount and timing of resources our collaborative partners may devote to our product candidates. Our collaborative partners may separately pursue competing product candidates, therapeutic approaches or technologies to develop treatments for the diseases targeted by us or our collaborative efforts, or may decide, for reasons not known to us, to discontinue development of product candidates under our agreements with them. Any of our collaborative partners may slow or discontinue the development of a product candidate covered by a collaborative arrangement for reasons that can include, but are not limited to:

•

a change in the collaborative partner's strategic focus as a result of merger, management changes, adverse business events, or other causes;



•

a change in the priority of the product candidate relative to other programs in the collaborator's pipeline;



•

a reassessment of the patent situation related to the compound or its target;



•

a change in the anticipated competition for the product candidate;



•

preclinical studies and clinical trial results; and



•

a reduction in the financial resources the collaborator can or is willing to apply to the development of new compounds.

        Even if our collaborative partners continue their collaborative arrangements with us, they may nevertheless determine not to actively pursue the development or commercialization of any resulting products. Also, our collaborative partners may fail to perform their obligations under the collaborative agreements or may be slow in performing their obligations. Our collaborative partners can terminate our collaborative agreements under certain conditions. The decision to advance a product that is covered by a collaborative agreement through clinical trials and ultimately to commercialization is in the discretion of our collaborative partners. If any collaborative partner were to terminate or breach our agreements, fail to complete its obligations to us in a timely manner, or decide to discontinue its development of a product candidate, our anticipated revenue from the agreement and from the development and commercialization of the products would be severely limited. If we are not able to establish additional collaborations or any or all of our existing collaborations are terminated and we are not able to enter into alternative collaborations on acceptable terms, or at all, our continued development, manufacture and commercialization of our product candidates could be delayed or scaled back as we may not have the funds or capability to continue these activities. If our collaborators fail to successfully develop and commercialize ADC compounds, our business prospects would be severely harmed.

We depend on a small number of collaborators for a substantial portion of our revenue. The loss of, or a material reduction in activity by, any one of these collaborators could result in a substantial decline in our revenue.

        We have and will continue to have collaborations with a limited number of companies. As a result, our financial performance depends on the efforts and overall success of these companies. Also, the failure of any one of our collaborative partners to perform its obligations under its agreement with us, including making any royalty, milestone or other payments to us, could have an adverse effect on our financial condition. Further, any material reduction by any one of our collaborative partners in its level of commitment of resources, funding, personnel, and interest in continued development under its agreement with us could have an adverse effect on our financial condition. Also, if consolidation trends in the healthcare industry continue, the number of our potential collaborators could decrease, which could have an adverse impact on our development efforts. If a present or future collaborator of ours were to be involved in a business combination, the collaborator's continued pursuit and emphasis on our product development program could be delayed, diminished or terminated.

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Royalties from commercial sales of Kadcyla will likely fluctuate and will impact our reported royalty revenues and rights to receive future payments from the commercial sale of Kadcyla under our license agreement with Roche and our royalty purchase agreement with Immunity Royalty Holdings, L.P.

        Roche's Kadcyla is currently the only product with respect to which we are entitled to receive royalties that has received marketing approval. In April 2015, Immunity Royalty Holdings, L.P. paid us $200 million to purchase our right to receive 100% of the royalty payments on commercial sales of Kadcyla arising under our development and commercialization license with Roche, through its Genentech unit, until Immunity Royalty Holdings has received aggregate Kadcyla royalties equal to $235 million or $260 million, depending on when the aggregate Kadcyla royalties received by Immunity Royalty Holdings reach a specified milestone. Once the applicable threshold is met, if ever, we will thereafter receive 85% and Immunity Royalty Holdings will receive 15% of the Kadcyla royalties for the remaining royalty term. These royalty revenues may fluctuate considerably because they depend upon, among other things, the rate of growth of sales of Kadcyla as well as the mix of U.S.-based sales and ex-U.S.-based sales and our valid patent claims. While the royalty purchase transaction with Immunity Royalty Holdings has mitigated any impact that fluctuations in these royalty revenues may have on our financial condition, negative fluctuations could delay, diminish or eliminate our right to resume receiving 85% of the royalty in the future, as described above.

Royalty rates under our license agreements with our collaborators may vary over the royalty term depending on our intellectual property rights and the presence of competing products.

        Most of our license agreements with our collaborators provide that the royalty rates are subject to downward adjustment in the absence of ImmunoGen patent rights covering various aspects of the manufacture, use or sale of the products developed under such licenses, or in the presence of competition from certain third-party products. For example, we expect the royalty rate for Sanofi's isatuximab anti-CD38 naked antibody compound to be reduced to low single digits because of (1) competitor development of alternative anti-CD38 antibody compounds, and (2) the lack of ImmunoGen patent rights covering isatuximab, since our ADC-related patent rights do not pertain to the compound and our isatuximab -specific patent rights were assigned to Sanofi under the terms of the applicable license.

We depend on our collaborative partners for the determination of royalty payments. We may not be able to detect errors and payment calculations may call for retroactive adjustments.

        The royalty payments we receive are determined by our collaborative partners based on their reported net sales. Each collaborative partner's calculation of the royalty payments is subject to and dependent upon the adequacy and accuracy of its sales and accounting functions, and errors may occur from time to time in the calculations made by a collaborative partner. Our agreement with Genentech provides us the right to audit the calculations and sales data for the associated royalty payments related to sales of Kadcyla; however, such audits may occur many months following our recognition of the royalty revenue, may require us to adjust our royalty revenues in later periods and generally require audit-related cost on our part.

If our collaborative partners' requirements for clinical materials to be manufactured by us are significantly lower than we have estimated, our financial results and condition could be adversely affected.

        We procure certain components of finished conjugate, including DM1, DM4, and linker, on behalf of several of our collaborators. In order to meet our commitments to our collaborative partners, we are required to enter into agreements with third parties to produce these components well in advance of our production of clinical materials on behalf of our collaborative partners. If our collaborative partners do not require as much clinical material as we have contracted to produce and we are unable to use

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these materials for our own products, we may not be able to recover our investment in these components and we may suffer losses. Collaborators have discontinued development of product candidates in the past and in the periods subsequent to these discontinuations, we had significantly reduced demand for DM1 and DM4 which adversely impacted our financial results.

        In addition, we operate a conjugate manufacturing facility. A portion of the cost of operating this facility, including the cost of manufacturing personnel, is reimbursed by our collaborators based on the number of batches of preclinical and clinical materials produced on their behalf. If we produce fewer batches of clinical materials for our collaborators, a smaller amount of the cost of operating the conjugate manufacturing facility will be charged to our collaborative partners and our financial condition could be adversely affected.

If our product requirements for clinical trials are significantly higher than we estimated, the inability to procure additional antibody or fill/finish services in a timely manner could impair our ability to initiate or advance our clinical trials.

        We rely on third-party suppliers to manufacture antibodies used in our own proprietary compounds. Due to the specific nature of the antibody and availability of production capacity, there is significant lead time required by these suppliers to provide us with the needed materials. If our antibody requirements for clinical materials to be manufactured are significantly higher than we estimated, we may not be able to readily procure additional antibody which would impair our ability to advance our clinical trials currently in process or initiate additional trials. We also rely on third parties to convert the bulk drug substance we manufacture into filled and finished vials of drug product for clinical use. Unanticipated difficulties or delays in the fill/finish process could impair our ability to advance our clinical trials currently in process or initiate additional trials. There can be no assurance that we will not have supply problems that could delay or stop our clinical trials or otherwise could have a material adverse effect on our business.

We currently rely on one third-party manufacturer with commercial production experience to produce our cell-killing agents, DM1 and DM4.

        We rely on a third-party supplier to manufacture one of the materials used to make ADC compounds. Our cell-killing agents DM1 and DM4, collectively DMx, are manufactured from a precursor, ansamitocin P3. We currently use a single supplier, Societá Italiana Corticosteroidi S.r.l., that converts ansamitocin P3 to DMx. Any delay or interruption in our supply of DMx could lead to a delay or interruption in our manufacturing operations, preclinical studies and clinical trials of our product candidates and our collaborators' product candidates, which could negatively affect our business.

We may be delayed or unable to establish the manufacturing capabilities necessary to develop and commercialize our and our collaborative partners' potential products.

        Currently, we have one conjugate manufacturing facility that we use to manufacture conjugated compounds for us and several of our collaborative partners for preclinical studies and early-stage clinical testing. Several of our partners have contracted for separate, large-scale manufacturing capacity to make materials to support potential future commercialization of their ADC compounds. We do not currently have the manufacturing capacity needed to make our product candidates for commercial sale. In addition, our manufacturing capacity may be insufficient to complete all clinical trials contemplated by us and our collaborative partners over time. We intend to rely in part on third-party contract manufacturers to produce sufficiently large quantities of drug materials that are and will be needed for later-stage clinical trials and commercialization of our potential products. We are currently in the process of developing relationships with third-party manufacturers that we believe will be necessary to continue the development of our product candidates. Third-party manufacturers may not be able to meet our needs with respect to timing, quantity or quality of materials. If we are unable to contract for

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a sufficient supply of needed materials on acceptable terms, or if we should encounter delays or difficulties in our relationships with manufacturers, our clinical trials may be delayed, thereby delaying the submission of product candidates for regulatory approval and the market introduction and subsequent commercialization of our potential products. Any such delays may lower our revenues and potential profitability.

We have one conjugate manufacturing facility and any prolonged and significant disruption at that facility could impair our ability to manufacture our and our collaborative partners' product candidates for clinical testing.

        Currently, in certain cases, we are contractually obligated to manufacture Phase I and non-pivotal Phase II clinical products for companies licensing our ADC technology. We manufacture this material, as well as material for our own product candidates, in our conjugate manufacturing facility. We have only one such manufacturing facility in which we can manufacture clinical products. Our current manufacturing facility contains highly specialized equipment and utilizes complex production processes developed over a number of years that would be difficult, time-consuming and costly to duplicate. Any prolonged disruption in the operations of our manufacturing facility would have a significant negative impact on our ability to manufacture products for clinical testing on our own and would cause us to seek additional third-party manufacturing contracts, thereby increasing our development costs. Even though we carry business interruption insurance policies, we may suffer losses as a result of business interruptions that exceed the coverage available or any losses which may be excluded under our insurance policies. Certain events, such as natural disasters, fire, political disturbances, sabotage or business accidents, which could impact our current or future facilities, could have a significant negative impact on our operations by disrupting our product development efforts until such time as we are able to repair our facility or put in place third-party contract manufacturers to assume this manufacturing role.

Unfavorable pricing regulations, third-party reimbursement practices or healthcare reform initiatives applicable to our product candidates could limit our potential product revenue.

        Antibody-based anticancer products are often much more costly to produce than traditional chemotherapeutics and tend to have significantly higher prices. Factors that help justify the price include the high mortality associated with many types of cancer and the need for more and better treatment options.

        Regulations governing drug pricing and reimbursement vary widely from country to country. Some countries require approval of the sales price of a drug before it can be marketed. Some countries restrict the physicians that can authorize the use of more expensive medications. Some countries establish treatment guidelines to help limit the use of more expensive therapeutics and the pool of patients that receive them. In some countries, including the U.S., third-party payers frequently seek discounts from list prices and are increasingly challenging the prices charged for medical products. Because our product candidates are in the development stage, we do not know the level of reimbursement, if any, we will receive for any products that we are able to successfully develop. If the reimbursement for any of our product candidates is inadequate in light of our development and other costs, our ability to achieve profitability would be affected.

        We believe that the efforts of governments and third-party payors to contain or reduce the cost of healthcare will continue to affect the business and financial condition of pharmaceutical and biopharmaceutical companies. A number of legislative and regulatory proposals to change the healthcare system in the U.S. and other major healthcare markets have been proposed and adopted in recent years. For example, the U.S. Congress enacted a limited prescription drug benefit for Medicare recipients as part of the Medicare Prescription Drug, Improvement and Modernization Act of 2003. While the program established by this statute may increase demand for any products that we are able

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to successfully develop, if we participate in this program, our prices will be negotiated with drug procurement organizations for Medicare beneficiaries and are likely to be lower than prices we might otherwise obtain. Non-Medicare third-party drug procurement organizations may also base the price they are willing to pay on the rate paid by drug procurement organizations for Medicare beneficiaries. The PPACA will also require discounts under the Medicare drug benefit program and increased rebates on drugs covered by Medicaid. In addition, the PPACA imposes an annual fee, which will increase annually, on sales by branded pharmaceutical manufacturers. The financial impact of these discounts, increased rebates and fees and the other provisions of the PPACA on our business is unclear and there can be no assurance that our business will not be materially adversely affected by the PPACA. In addition, ongoing initiatives in the U.S. have increased and will continue to increase pressure on drug pricing. The announcement or adoption of any such initiative could have an adverse effect on potential revenues from any product candidate that we may successfully develop.

We may be unable to establish sales and marketing capabilities necessary to successfully commercialize our potential products.

        We currently have no direct sales or marketing capabilities. We may rely on third parties to market and sell most of our primary product candidates or we may outlicense these products prior to the time when these capabilities are needed. If we decide to market our potential products through a direct sales force, we would need either to hire a sales force with expertise in pharmaceutical sales or to contract with a third party to provide a sales force which meets our needs. We may be unable to establish marketing, sales and distribution capabilities necessary to commercialize and gain market acceptance for our potential products and be competitive. In addition, co-promotion or other marketing arrangements with third parties to commercialize potential products could significantly limit the revenues we derive from these potential products, and these third parties may fail to commercialize our compounds successfully.

If our product candidates or those of our collaborative partners do not gain market acceptance, our business will suffer.

        Even if clinical trials demonstrate the safety and efficacy of our and our collaborative partners' product candidates and the necessary regulatory approvals are obtained, our and our collaborative partners' products may not gain market acceptance among physicians, patients, healthcare payors and other members of the medical community. The degree of market acceptance of any products that we or our collaborative partners develop will depend on a number of factors, including:

•

their level of clinical efficacy and safety;



•

their advantage over alternative treatment methods;



•

our/the marketer's and our collaborative partners' ability to gain acceptable reimbursement and the reimbursement policies of government and third-party payors; and



•

the quality of the distribution capabilities of the party(ies) responsible to market and distribute the product(s).

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        Physicians may not prescribe any of our future products until such time as clinical data or other factors demonstrate the safety and efficacy of those products as compared to conventional drugs and other treatments. Even if the clinical safety and efficacy of therapies using our products is established, physicians may elect not to recommend the therapies for any number of other reasons, including whether the mode of administration of our products is effective for certain conditions, and whether the physicians are already using competing products that satisfy their treatment objectives. Physicians, patients, third-party payors and the medical community may not accept and use any product candidates that we, or our collaborative partners, develop. If our products do not achieve significant market acceptance and use, we will not be able to recover the significant investment we have made in developing such products and our business will be severely harmed.

We may be unable to compete successfully.

        The markets in which we compete are well established and intensely competitive. We may be unable to compete successfully against our current and future competitors. Our failure to compete successfully may result in lower volume sold, pricing reductions, reduced gross margins and failure to achieve market acceptance for our potential products. Our competitors include research institutions, pharmaceutical companies and biotechnology companies, such as Pfizer, Seattle Genetics, Roche, Bristol-Myers Squibb and Takeda. Many of these organizations have substantially more experience and more capital, research and development, regulatory, manufacturing, human and other resources than we do. As a result, they may:

•

develop products that are safer or more effective than our product candidates;



•

obtain FDA and other regulatory approvals or reach the market with their products more rapidly than we can, reducing the potential sales of our product candidates;



•

devote greater resources to market or sell their products;



•

adapt more quickly to new technologies and scientific advances;



•

initiate or withstand substantial price competition more successfully than we can;



•

have greater success in recruiting skilled scientific workers from the limited pool of available talent;



•

more effectively negotiate third-party licensing and collaboration arrangements; and



•

take advantage of acquisitions or other opportunities more readily than we can.

        A number of pharmaceutical and biotechnology companies are currently developing products targeting the same types of cancer that we target, and some of our competitors' products have entered clinical trials or already are commercially available.

        Our product candidates, if approved and commercialized, will also compete against well-established, existing, therapeutic products that are currently reimbursed by government healthcare programs, private health insurers and health maintenance organizations. In addition, if our product candidates are approved and commercialized, we may face competition from biosimilars. The route to market for biosimilars was established with the passage of the PPACA in March 2010. The PPACA establishes a pathway for the FDA approval of follow-on biologics and provides twelve years data exclusivity for reference products and an additional six months exclusivity period if pediatric studies are conducted. In Europe, the European Medicines Agency has issued guidelines for approving products through an abbreviated pathway, and biosimilars have been approved in Europe. If a biosimilar version of one of our potential products were approved in the U.S. or Europe, it could have a negative effect on sales and gross profits of the potential product and our financial condition.

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        We face and will continue to face intense competition from other companies for collaborative arrangements with pharmaceutical and biotechnology companies, for relationships with academic and research institutions and for licenses to proprietary technology. In addition, we anticipate that we will face increased competition in the future as new companies enter our markets and as scientific developments surrounding antibody-based therapeutics for cancer continue to accelerate. While we will seek to expand our technological capabilities to remain competitive, research and development by others may render our technology or product candidates obsolete or noncompetitive or result in treatments or cures superior to any therapy developed by us.

If we are unable to protect our intellectual property rights adequately, the value of our technology and our product candidates could be diminished.

        Our success depends in part on obtaining, maintaining and enforcing our patents and other proprietary rights and our ability to avoid infringing the proprietary rights of others. Patent law relating to the scope of claims in the biotechnology field in which we operate is still evolving, is surrounded by a great deal of uncertainty and involves complex legal, scientific and factual questions. To date, no consistent policy has emerged regarding the breadth of claims allowed in biotechnology patents. Accordingly, our pending patent applications may not result in issued patents or in patent claims as broad as in the original applications. Although we own numerous patents, the issuance of a patent is not conclusive as to its validity or enforceability. Through litigation, a third party may challenge the validity or enforceability of a patent after its issuance.

        Patents and applications owned or licensed by us may become the subject of interference, opposition, nullity, or other proceedings in a court or patent office in the U.S. or in a foreign jurisdiction to determine validity, enforceability or priority of invention, which could result in substantial cost to us. An adverse decision in such a proceeding may result in our loss of rights under a patent or patent application. It is unclear how much protection, if any, will be given to our patents if we attempt to enforce them or if they are challenged in court or in other proceedings. A competitor may successfully invalidate our patents or a challenge could result in limitations of the patents' coverage. In addition, the cost of litigation or interference proceedings to uphold the validity of patents can be substantial. If we are unsuccessful in these proceedings, third parties may be able to use our patented technology without paying us licensing fees or royalties. Moreover, competitors may infringe our patents or successfully avoid them through design innovation. To prevent infringement or unauthorized use, we may need to file infringement claims, which are expensive and time-consuming. In an infringement proceeding, a court may decide that a patent of ours is not valid. Even if the validity of our patents were upheld, a court may refuse to stop the other party from using the technology at issue on the ground that its activities are not covered by our patents.

        The Leahy-Smith America Invents Act was signed into law on September 16, 2011, and became fully effective in March 2013. In general, the legislation attempts to address issues surrounding the enforceability of patents and the increase in patent litigation by, among other things, moving to a first inventor-to-file system, establishing new procedures for challenging patents and establishing different methods for invalidating patents. Governmental rule-making implementing the new statute is evolving and will continue to introduce new substantive rules and procedures, particularly with regard to post-grant proceedings such as inter partes review and post-grant review. In due course, the courts will interpret various aspects of the law and related agency rules in ways that we cannot predict, potentially making it easier for competitors and other interested parties to challenge our patents, which, if successful, could have a material adverse effect on our business and prospects. In addition, as the United States Supreme Court has become increasingly active in reviewing U.S. patent law in recent years, and the extent to which their recent decisions will affect our ability to enforce certain types of claims under our U.S. patents or obtain future patents in certain areas is difficult to predict at this time.

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        Policing unauthorized use of our intellectual property is difficult, and we may not be able to prevent misappropriation of our proprietary rights, particularly in countries where the laws may not protect such rights as fully as in the U.S.

        In addition to our patent rights, we also rely on unpatented technology, trade secrets, know-how and confidential information. Third parties may independently develop substantially equivalent information and techniques or otherwise gain access to or disclose our technology. We may not be able to effectively protect our rights in unpatented technology, trade secrets, know-how and confidential information. We require each of our employees, consultants and corporate partners to execute a confidentiality agreement at the commencement of an employment, consulting or collaborative relationship with us. Further, we require that all employees enter into assignment of invention agreements as a condition of employment. However, these agreements may not provide effective protection of our information or, in the event of unauthorized use or disclosure, they may not provide adequate remedies.

Any inability to license proprietary technologies or processes from third parties which we use in connection with the development and manufacture of our product candidates may impair our business.

        Other companies, universities and research institutions have or may obtain patents that could limit our ability to use, manufacture, market or sell our product candidates or impair our competitive position. As a result, we would have to obtain licenses from other parties before we could continue using, manufacturing, marketing or selling our potential products. Any necessary licenses may not be available on commercially acceptable terms, if at all. If we do not obtain required licenses, we may not be able to market our potential products at all or we may encounter significant delays in product development while we redesign products or methods that are found to infringe on the patents held by others.

We may incur substantial costs as a result of litigation or other proceedings relating to patent and other intellectual property rights held by third parties and we may be unable to protect our rights to, or to commercialize, our product candidates.

        Patent litigation is very common in the biotechnology and pharmaceutical industries. Third parties may assert patent or other intellectual property infringement claims against us with respect to our technologies, products or other matters. From time to time, we have received correspondence from third parties alleging that we infringe their intellectual property rights. Any claims that might be brought against us alleging infringement of patents may cause us to incur significant expenses and, if successfully asserted against us, may cause us to pay substantial damages and limit our ability to use the intellectual property subject to these claims. Even if we were to prevail, any litigation would be costly and time-consuming and could divert the attention of our management and key personnel from our business operations. Furthermore, as a result of a patent infringement suit, we may be forced to stop or delay developing, manufacturing or selling potential products that incorporate the challenged intellectual property unless we enter into royalty or license agreements. There may be third-party patents, patent applications and other intellectual property relevant to our potential products that may block or compete with our products or processes. In addition, we sometimes undertake research and development with respect to potential products even when we are aware of third-party patents that may be relevant to our potential products, on the basis that such patents may be challenged or licensed by us. If our subsequent challenge to such patents were not to prevail, we may not be able to commercialize our potential products after having already incurred significant expenditures unless we are able to license the intellectual property on commercially reasonable terms. We may not be able to obtain royalty or license agreements on terms acceptable to us, if at all. Even if we were able to obtain licenses to such technology, some licenses may be non-exclusive, thereby giving our competitors access to the same technologies licensed to us. Ultimately, we may be unable to commercialize some of our

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potential products or may have to cease some of our business operations, which could severely harm our business.

We use hazardous materials in our business, and any claims relating to improper handling, storage or disposal of these materials could harm our business.

        Our research and development and manufacturing activities involve the controlled use of hazardous materials, chemicals, biological materials and radioactive compounds. We are subject to federal, state and local laws and regulations governing the use, manufacture, storage, handling and disposal of these materials and certain waste products. Although we believe that our safety procedures for handling and disposing of these materials comply with the standards prescribed by applicable laws and regulations, we cannot completely eliminate the risk of accidental contamination or injury from these materials. In the event of such an accident, we could be held liable for any resulting damages, and any liability could exceed our resources. We may be required to incur significant costs to comply with these laws in the future. Failure to comply with these laws could result in fines and the revocation of permits, which could prevent us from conducting our business.

We face product liability risks and may not be able to obtain adequate insurance.

        While we secure waivers from all participants in our clinical trials, the use of our product candidates during testing or after approval entails an inherent risk of adverse effects, which could expose us to product liability claims. Regardless of their merit or eventual outcome, product liability claims may result in:

•

decreased demand for our product;



•

injury to our reputation and significant negative media attention;



•

withdrawal of clinical trial volunteers;



•

costs of litigation;



•

distraction of management; and



•

substantial monetary awards to plaintiffs.

        We may not have sufficient resources to satisfy any liability resulting from these claims. We currently have product liability insurance for products which are in clinical testing, however, our coverage may not be adequate in scope to protect us in the event of a successful product liability claim. Further, we may not be able to maintain our current insurance or obtain general product liability insurance on reasonable terms and at an acceptable cost if we or our collaborative partners begin commercial production of our proposed product candidates. This insurance, even if we can obtain and maintain it, may not be sufficient to provide us with adequate coverage against potential liabilities.

We depend on our key personnel and we must continue to attract and retain key employees and consultants.

        We depend on our key scientific and management personnel. Our ability to pursue the development of our current and future product candidates depends largely on retaining the services of our existing personnel and hiring additional qualified scientific personnel to perform research and development. We will also need to hire personnel with expertise in clinical testing, government regulation, manufacturing, marketing and finance. Attracting and retaining qualified personnel will be critical to our success. We may not be able to attract and retain personnel on acceptable terms given the competition for such personnel among biotechnology, pharmaceutical and healthcare companies, universities and non-profit research institutions. Failure to retain our existing key management and

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scientific personnel or to attract additional highly qualified personnel could delay the development of our product candidates and harm our business.

Our stock price can fluctuate significantly and results announced by us and our collaborators can cause our stock price to decline.

        Our stock price can fluctuate significantly due to business developments announced by us and by our collaborators, or as a result of market trends and daily trading volume. The business developments that could impact our stock price include disclosures related to clinical findings with compounds that make use of our ADC technology, new collaborations and clinical advancement or discontinuation of product candidates that make use of our ADC technology. Our stock price can also fluctuate significantly with the level of overall investment interest in small-cap biotechnology stocks.

        Our operating results have fluctuated in the past and are likely to continue to do so in the future. Our revenue is unpredictable and may fluctuate due to the timing of non-recurring licensing fees, decisions of our collaborative partners with respect to our agreements with them, reimbursement for manufacturing services, the achievement of milestones and our receipt of the related milestone payments under new and existing licensing and collaboration agreements. Revenue historically recognized under our prior collaboration agreements may not be an indicator of revenue from any future collaboration. In addition, our expenses are unpredictable and may fluctuate from quarter to quarter due to the timing of expenses, which may include obligations to manufacture or supply product or payments owed by us under licensing or collaboration agreements. It is possible that our quarterly and/or annual operating results will not meet the expectations of securities analysts or investors, causing the market price of our common stock to decline. We believe that quarter-to-quarter and year-to-year comparisons of our operating results are not good indicators of our future performance and should not be relied upon to predict the future performance of our stock price.

The potential sale of additional shares of our common stock may cause our stock price to decline.

        Pursuant to shelf registration statements filed with the Securities and Exchange Commission, in fiscal 2012, we sold 6,250,000 shares of our common stock at $16.00 per share in a public offering resulting in gross proceeds of $100 million; in fiscal 2011, we sold 7,800,000 shares of our common stock at $12.00 per share in a public offering resulting in gross proceeds of $93.6 million; in fiscal 2010, we sold 10,350,000 shares of our common stock at $8.00 per share in a public offering resulting in gross proceeds of $82.8 million; and in fiscal 2009, we sold 5,750,000 shares of our common stock at $7.00 per share in a public offering resulting in gross proceeds of $40.3 million. The potential sale of additional shares of our common stock may be dilutive to our shares outstanding and may cause our stock price to decline.

We do not intend to pay cash dividends on our common stock.

        We have not paid cash dividends since our inception and do not intend to pay cash dividends in the foreseeable future. Therefore, shareholders will have to rely on appreciation in our stock price, if any, in order to achieve a gain on an investment.

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A WARNING ABOUT FORWARD-LOOKING STATEMENTS

        This report includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These statements relate to analyses and other information which are based on forecasts of future results and estimates of amounts that are not yet determinable. These statements also relate to our future prospects, developments and business strategies.

        These forward-looking statements are identified by their use of terms and phrases, such as "anticipate," "believe," "could," "estimate," "expect," "intend," "may," "plan," "predict," "project," "will" and other similar terms and phrases, including references to assumptions. These statements are contained in the "Business," "Risk Factors" and "Management's Discussion and Analysis of Financial Condition and Results of Operations" sections, as well as other sections of this Annual Report on Form 10-K.

        These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause actual results to be materially different from those contemplated by our forward-looking statements. These known and unknown risks, uncertainties and other factors are described in detail in the "Risk Factors" section and in other sections of this Annual Report on Form 10-K. We disclaim any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

Item 1B.    Unresolved Staff Comments

        None.

Item 2.    Properties

        We lease approximately 108,000 square feet of laboratory and office space in a building located at 830 Winter Street, Waltham, MA. The term of the 830 Winter Street lease expires on March 31, 2026, with an option for us to extend the lease for two additional five-year terms. We also lease approximately 43,850 square feet of space at 333 Providence Highway, Norwood, MA, which serves as our conjugate manufacturing facility and office space. The 333 Providence Highway lease expires on June 30, 2018, with an option for us to extend the lease for an additional five-year term. Due to space requirements, in April 2013, we entered into a lease agreement for the rental of 7,507 square feet of office space at 100 River Ridge Drive, Norwood, MA. The initial term of the lease is for five years and two months commencing in July 2013 with an option for us to extend the lease for an additional five-year term. We entered into a sublease in December 2014 for this space, effective January 2015 through the remaining initial term of the lease.

Item 3.    Legal Proceedings

        From time to time we may be a party to various legal proceedings arising in the ordinary course of our business. We are not currently subject to any material legal proceedings.

Item 3.1.    Executive Officers of the Registrant

        ImmunoGen's executive officers are appointed by the Board of Directors at the first meeting of the Board following the annual meeting of shareholders or at other Board meetings as appropriate, and hold office until the first Board meeting following the next annual meeting of shareholders and until a successor is chosen, subject to prior death, resignation or removal. Information regarding our executive officers is presented below.

        Daniel M. Junius, age 63, joined ImmunoGen in 2005, and has served as our President and Chief Executive Officer since 2009. Mr. Junius has also served as a director of ImmunoGen since 2008 and is

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a director of IDEXX Laboratories, Inc. Mr. Junius holds a Masters of Management from Northwestern University's Kellogg School of Management.

        Richard J. Gregory, age 57, joined ImmunoGen in January 2015, and has served as our Executive Vice President and Chief Scientific Officer since that date. Prior to joining ImmunoGen, he spent 25 years at Genzyme Corporation, a biotechnology company, in roles of increasing responsibility, including Senior Vice President and Head of Research from 2003 until Genzyme's acquisition by Sanofi in 2011, and Head of Research and Development for Genzyme from 2011 through 2014. Dr. Gregory holds a PhD from the University of Massachusetts, Amherst, and completed his post-doctoral work at the Worcester Foundation for Experimental Biology.

        John M. Lambert, PhD, age 64, joined ImmunoGen in 1987, and has served as Executive Vice President and Distinguished Research Fellow since January 2015. Prior to that he served as our Executive Vice President and Chief Scientific Officer from 2008 through 2014. Dr. Lambert holds a PhD in Biochemistry from University of Cambridge in England, and completed his postdoctoral work at the University of California at Davis and at Glasgow University in Scotland.

        David B. Johnston, age 60, joined ImmunoGen in 2013, and has served as our Executive Vice President and Chief Financial Officer since that date. Prior to joining ImmunoGen, Mr. Johnston served as Chief Financial Officer of AVEO Pharmaceuticals, Inc., a biotechnology company, from 2007 to 2013. Mr. Johnston holds a Master of Business Administration from the University of Michigan.

        Charles Q. Morris, MB, ChB, MRCP (UK), age 50, joined ImmunoGen in November 2012, and has served as our Executive Vice President and Chief Development Officer since that date. Prior to joining ImmunoGen, he served as Executive Vice President and Chief Medical Officer of Allos Therapeutics, Inc., a biotechnology company, from 2010 until its acquisition in 2012. Prior to that he served as Vice President, Worldwide Clinical Research, at Cephalon, Inc., a biotechnology company, from 2008 to 2010. Dr. Morris holds his medical degrees from Sheffield University Medical School and is a member of the Royal College of Physicians of London.

        Sandra Poole, age 51, joined ImmunoGen in September 2014, and has served as our Executive Vice President of Technical Operations since July 1, 2015. Prior to that she served as our Senior Vice President, Technical Operations, from her date of hire through June 2015. Prior to joining ImmunoGen, she spent 15 years at Genzyme Corporation, a biotechnology company, and its subsidiaries in roles of increasing responsibility, including as Senior Vice President overseeing various technical operations within Genzyme from 2009 to 2013, and as Senior Vice President, Biologics Manufacturing from 2013 to September 2014.

        Craig Barrows, age 60, joined ImmunoGen in 2007, and has served as our Vice President, General Counsel and Secretary since that date.

        Ellie Harrison, age 60, joined ImmunoGen in February 2014, and has served as our Vice President and Chief Human Resources Officer since that date. Prior to joining ImmunoGen, she served as Senior Vice President of Human Resources of Blue Cross and Blue Shield of Rhode Island, a healthcare provider, from 2013 to February 2014. Prior to that she served as a Managing Director and Senior Human Resources Advisor to the global consumer banking organization of Citigroup, a financial institution, from 2009 to 2012.

        Peter J. Williams, age 61, joined ImmunoGen in August 2009, and has served as our Vice President, Business Development since that date.

Item 4.    Mine Safety Disclosures

        None.

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PART II

Item 5.    Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

Market Price of Our Common Stock and Related Stockholder Matters

        Our common stock is quoted on the NASDAQ Global Select Market under the symbol "IMGN." The table below sets forth the high and low closing price per share of our common stock as reported by NASDAQ:

        As of August 20, 2015, the closing price per share of our common stock was $12.47, as reported by NASDAQ, and we had approximately 470 holders of record of our common stock.

        We have not paid any cash dividends on our common stock since our inception and do not intend to pay any cash dividends in the foreseeable future.

Equity Compensation Plan Information (in thousands)

Recent Sales of Unregistered Securities; Uses of Proceeds from Registered Securities; Issuer Repurchases of Equity Securities

        None.

Item 6.    Selected Financial Data

        The following table (in thousands, except per share data) sets forth our consolidated financial data for each of our five fiscal years through our fiscal year ended June 30, 2015. The information set forth below should be read in conjunction with "Management's Discussion and Analysis of Financial

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Condition and Results of Operations" and the consolidated financial statements and related notes included elsewhere in this Annual Report on Form 10-K.

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Item 7.    Management's Discussion and Analysis of Financial Condition and Results of Operations

Overview

        Since our inception, we have been principally engaged in the development of novel, antibody-drug conjugates, or ADCs, for the treatment of cancer using our expertise in cancer biology, monoclonal antibodies, highly potent cytotoxic, or cell-killing, agents, and the design of linkers that enable these agents to remain stably attached to the antibodies while in the blood stream and released in their fully active form after delivery to a cancer cell. An anticancer compound made using our ADC technology consists of a monoclonal antibody that binds specifically to an antigen target found on the surface of cancer cells with one of our proprietary cell-killing agents attached to the antibody using one of our engineered linkers. Its antibody component enables an ADC compound to bind specifically to cancer cells that express its target antigen, the highly potent cytotoxic agent serves to kill the cancer cell, and the engineered linker controls the release and activation of the cytotoxic agent inside the cancer cell. With some ADC compounds, the antibody component also has anticancer activity of its own. Our ADC technology is designed to enable the creation of highly effective, well-tolerated anticancer products. All of the ADC compounds currently in clinical testing contain either DM1 or DM4 as the cytotoxic agent. Both DM1 and DM4, collectively DMx, are our proprietary derivatives of a cytotoxic agent called maytansine. We also have developed agents we call IGNs, one of which, DGN462, is used in our preclinical compound IMGN779.

        We use our proprietary ADC technology in conjunction with our in-house antibody expertise to develop our own anticancer product candidates. We also enter into agreements that enable companies to use our ADC technology to develop and commercialize product candidates to specified targets. Under the terms of our agreements, we are generally entitled to upfront fees, milestone payments, and royalties on any commercial product sales. In addition, under certain agreements we are compensated for research and development activities performed at our collaborative partner's request at negotiated prices which are generally consistent with what other third parties would charge. We are compensated to manufacture preclinical and clinical materials and deliver cytotoxic agent material at negotiated prices which are generally consistent with what other third parties would charge. Currently, our partners include Amgen, Bayer HealthCare, Biotest, Lilly, Novartis, Roche, Sanofi and Takeda. We also have a research agreement with CytomX Therapeutics that allows each company to develop probody-drug conjugates against a specified number of cancer targets using CytomX's Probody™ antibody masking technology with our payload agents and engineered linkers. We expect that substantially all of our revenue for the foreseeable future will result from payments under our collaborative arrangements. Details for some of our major and recent collaborative agreements can be found in this Form 10-K under Item 1. Business.

        To date, we have not generated revenues from commercial sales of internal products and we expect to incur significant operating losses for the foreseeable future. As of June 30, 2015, we had approximately $278.1 million in cash and cash equivalents compared to $142.3 million as of June 30, 2014.

        We anticipate that future cash expenditures will be partially offset by collaboration-derived proceeds, including milestone payments and upfront fees. Accordingly, period-to-period cash balances may fluctuate dramatically based upon the timing of receipt of the proceeds. We believe that our established collaborative agreements, while subject to specified milestone achievements, will provide funding to assist us in meeting obligations under our collaborative agreements while also assisting in providing funding for the development of internal product candidates and technologies. However, we can give no assurances that such collaborative agreement funding will, in fact, be realized in the time frames we expect, or at all. Should we or our partners not meet some or all of the terms and conditions of our various collaboration agreements, we may be required to secure alternative financing arrangements, find additional partners and/or defer or limit some or all of our research, development

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and/or clinical projects. However, we cannot provide assurance that any such opportunities presented by additional partners or alternative financing arrangements will be entirely available to us, if at all.

Critical Accounting Policies

        We prepare our consolidated financial statements in accordance with accounting principles generally accepted in the U.S. The preparation of these financial statements requires us to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosure of contingent assets and liabilities. On an on-going basis, we evaluate our estimates, including those related to our collaborative agreements, clinical trial accruals, inventory and stock-based compensation. We base our estimates on historical experience and various other assumptions that we believe to be reasonable under the circumstances. Actual results may differ from these estimates.

        We believe the following critical accounting policies reflect our more significant judgments and estimates used in the preparation of our consolidated financial statements.

Revenue Recognition

        We enter into licensing and development agreements with collaborative partners for the development of monoclonal antibody-based anticancer therapeutics. The terms of these agreements contain multiple deliverables which may include (i) licenses, or options to obtain licenses, to our ADC technology, (ii) rights to future technological improvements, (iii) research activities to be performed on behalf of the collaborative partner, (iv) delivery of cytotoxic agents and (v) the manufacture of preclinical or clinical materials for the collaborative partner. Payments to us under these agreements may include upfront fees, option fees, exercise fees, payments for research activities, payments for the manufacture of preclinical or clinical materials, payments based upon the achievement of certain milestones and royalties on product sales. We follow the provisions of the Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) Topic 605-25, "Revenue Recognition—Multiple-Element Arrangements," and ASC Topic 605-28, "Revenue Recognition—Milestone Method," in accounting for these agreements. In order to account for these agreements, we must identify the deliverables included within the agreement and evaluate which deliverables represent separate units of accounting based on whether certain criteria are met, including whether the delivered element has stand-alone value to the collaborator. The consideration received is allocated among the separate units of accounting, and the applicable revenue recognition criteria are applied to each of the separate units.

        At June 30, 2015, we had the following two types of agreements with the parties identified below:

•

Development and commercialization licenses, which provide the party with the right to use our ADC technology and/or certain other intellectual property to develop compounds to a specified antigen target:

Amgen (four exclusive single-target licenses*)

Bayer HealthCare (one exclusive single-target license)

Biotest (one exclusive single-target license)

Lilly (three exclusive single-target licenses)

Novartis (five exclusive single-target licenses and one license to two related targets: one target on an exclusive basis and the second target on a non-exclusive basis)

Roche, through its Genentech unit (five exclusive single-target licenses)

Sanofi (one exclusive single-target license and one exclusive license to multiple individual targets)

*

Amgen has sublicensed one of its exclusive single-target licenses to Oxford BioTherapeutics Ltd.

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•

Research license/option agreement for a defined period of time to secure development and commercialization licenses to use our ADC technology to develop anticancer compounds to specified targets on established terms (referred to herein as right-to-test agreements):

Sanofi

CytomX

Takeda

        There are no performance, cancellation, termination or refund provisions in any of the arrangements that contain material financial consequences to us.

Development and Commercialization Licenses

        The deliverables under a development and commercialization license agreement generally include the exclusive license to our ADC technology with respect to a specified antigen target, and may also include deliverables related to rights to future technological improvements, research activities to be performed on behalf of the collaborative partner and the manufacture of preclinical or clinical materials for the collaborative partner.

        Generally, development and commercialization licenses contain non-refundable terms for payments and, depending on the terms of the agreement, provide that we will (i) at the collaborator's request, provide research services at negotiated prices which are generally consistent with what other third parties would charge, (ii) at the collaborator's request, manufacture and provide to it preclinical and clinical materials or deliver cytotoxic agents at negotiated prices which are generally consistent with what other third parties would charge, (iii) earn payments upon the achievement of certain milestones and (iv) earn royalty payments, generally until the later of the last applicable patent expiration or 10 to 12 years after product launch. In the case of Kadcyla, however, the minimum royalty term is 10 years and the maximum royalty term is 12 years on a country-by-country basis, regardless of patent protection. Royalty rates may vary over the royalty term depending on our intellectual property rights and/or the presence of comparable competing products. We may provide technical assistance and share any technology improvements with our collaborators during the term of the collaboration agreements. We do not directly control when or whether any collaborator will request research or manufacturing services, achieve milestones or become liable for royalty payments. As a result, we cannot predict when or if we will recognize revenues in connection with any of the foregoing.

        In determining the units of accounting, management evaluates whether the license has stand-alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace. If we conclude that the license has stand-alone value and therefore will be accounted for as a separate unit of accounting, we then determine the estimated selling prices of the license and all other units of accounting based on market conditions, similar arrangements entered into by third parties, and entity-specific factors such as the terms of our previous collaborative agreements, recent preclinical and clinical testing results of therapeutic products that use our ADC technology, our pricing practices and pricing objectives, the likelihood that technological improvements will be made, and, if made, will be used by our collaborators and the nature of the research services to be performed on behalf of our collaborators and market rates for similar services.

        Upfront payments on development and commercialization licenses are deferred if facts and circumstances dictate that the license does not have stand-alone value. Prior to the adoption of Accounting Standards Update (ASU) No. 2009-13, "Revenue Arrangements with Multiple Deliverables" on July 1, 2010, we determined that our licenses lacked stand-alone value and were combined with other elements of the arrangement and any amounts associated with the license were

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deferred and amortized over a certain period, which we refer to as our period of substantial involvement. The determination of the length of the period over which to defer revenue is subject to judgment and estimation and can have an impact on the amount of revenue recognized in a given period. Historically our involvement with the development of a collaborator's product candidate has been significant at the early stages of development, and lessens as it progresses into clinical trials. Also, as a drug candidate gets closer to commencing pivotal testing our collaborators have sought an alternative site to manufacture their products, as our facility does not produce pivotal or commercial drug product. Accordingly, we generally estimate this period of substantial involvement to begin at the inception of the collaboration agreement and conclude at the end of non-pivotal Phase II testing. We believe this period of substantial involvement is, depending on the nature of the license, on average six and one-half years. Quarterly, we reassess our periods of substantial involvement over which we amortize our upfront license fees and make adjustments as appropriate. In the event a collaborator elects to discontinue development of a specific product candidate under a development and commercialization license, but retains its right to use our technology to develop an alternative product candidate to the same target or a target substitute, we would cease amortization of any remaining portion of the upfront fee until there is substantial preclinical activity on another product candidate and its remaining period of substantial involvement can be estimated. In the event that a development and commercialization license were to be terminated, we would recognize as revenue any portion of the upfront fee that had not previously been recorded as revenue, but was classified as deferred revenue, at the date of such termination.

        Subsequent to the adoption of ASU No. 2009-13, we determined that our research licenses lack stand-alone value and are considered for aggregation with the other elements of the arrangement and accounted for as one unit of accounting.

        Upfront payments on development and commercialization licenses may be recognized upon delivery of the license if facts and circumstances dictate that the license has stand-alone value from the undelivered elements, which generally include rights to future technological improvements, research services, delivery of cytotoxic agents and the manufacture of preclinical and clinical materials.

        We recognize revenue related to research services that represent separate units of accounting as they are performed, as long as there is persuasive evidence of an arrangement, the fee is fixed or determinable, and collection of the related receivable is probable. We recognize revenue related to the rights to future technological improvements over the estimated term of the applicable license.

        We may also provide cytotoxic agents to our collaborators or produce preclinical and clinical materials for them at negotiated prices which are generally consistent with what other third parties would charge. We recognize revenue on cytotoxic agents and on preclinical and clinical materials when the materials have passed all quality testing required for collaborator acceptance and title and risk of loss have transferred to the collaborator. Arrangement consideration allocated to the manufacture of preclinical and clinical materials in a multiple-deliverable arrangement is below our full cost, and our full cost is not expected to ever be below our contract selling prices for our existing collaborations. During the fiscal years ended June 30, 2015, 2014 and 2013, the difference between our full cost to manufacture preclinical and clinical materials on behalf of our collaborators as compared to total amounts received from collaborators for the manufacture of preclinical and clinical materials was $9.2 million, $2.3 million, and $755,000, respectively. The majority of our costs to produce these preclinical and clinical materials are fixed and then allocated to each batch based on the number of batches produced during the period. Therefore, our costs to produce these materials are significantly impacted by the number of batches produced during the period. The volume of preclinical and clinical materials we produce is directly related to the number of clinical trials we and our collaborators are preparing for or currently have underway, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period such trials last. Accordingly, the volume of preclinical and

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clinical materials produced, and therefore our per-batch costs to manufacture these preclinical and clinical materials, may vary significantly from period to period.

        We may also produce research material for potential collaborators under material transfer agreements. Additionally, we perform research activities, including developing antibody specific conjugation processes, on behalf of our collaborators and potential collaborators during the early evaluation and preclinical testing stages of drug development. We record amounts received for research materials produced or services performed as a component of research and development support revenue. We also develop conjugation processes for materials for later stage testing and commercialization for certain collaborators. We are compensated at negotiated rates and may receive milestone payments for developing these processes which are recorded as a component of research and development support revenue.

        Our development and commercialization license agreements have milestone payments which for reporting purposes are aggregated into three categories: (i) development milestones, (ii) regulatory milestones, and (iii) sales milestones. Development milestones are typically payable when a product candidate initiates or advances into different clinical trial phases. Regulatory milestones are typically payable upon submission for marketing approval with the FDA or other countries' regulatory authorities or on receipt of actual marketing approvals for the compound or for additional indications. Sales milestones are typically payable when annual sales reach certain levels.

        At the inception of each agreement that includes milestone payments, we evaluate whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether (a) the consideration is commensurate with either (1) the entity's performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity's performance to achieve the milestone, (b) the consideration relates solely to past performance and (c) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. We evaluate factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.

        Non-refundable development and regulatory milestones that are expected to be achieved as a result of our efforts during the period of substantial involvement are considered substantive and are recognized as revenue upon the achievement of the milestone, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive because we do not contribute effort to the achievement of such milestones are generally achieved after the period of substantial involvement and are recognized as revenue upon achievement of the milestone, as there are no undelivered elements remaining and no continuing performance obligations, assuming all other revenue recognition criteria are met.

        Under our development and commercialization license agreements, we receive royalty payments based upon our licensees' net sales of covered products. Generally, under these agreements we are to receive royalty reports and payments from our licensees approximately one quarter in arrears, that is, generally in the second month of the quarter after the licensee has sold the royalty bearing product or products. We recognize royalty revenues when we can reliably estimate such amounts and collectability is reasonably assured. As such, we generally recognize royalty revenues in the quarter reported to us by our licensees, or one quarter following the quarter in which sales by our licensees occurred.

Right-to-Test Agreements

        Our right-to-test agreements provide collaborators the right to (a) test our ADC technology for a defined period of time through a research, or right-to-test, license, (b) take options, for a defined

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period of time, to specified targets and (c) upon exercise of those options, secure or "take" licenses to develop and commercialize products for the specified targets on established terms. Under these agreements, fees may be due to us (i) at the inception of the arrangement (referred to as "upfront" fees or payments), (ii) upon taking an option with respect to a specific target (referred to as option fees or payments earned, if any, when the option is "taken"), (iii) upon the exercise of a previously taken option to acquire a development and commercialization license(s) (referred to as exercise fees or payments earned, if any, when the development and commercialization license is "taken"), or (iv) some combination of all of these fees.

        The accounting for right-to-test agreements is dependent on the nature of the option granted to the collaborative partner. Options are considered substantive if, at the inception of a right-to-test agreement, we are at risk as to whether the collaborative partner will choose to exercise the options to secure development and commercialization licenses. Factors that are considered in evaluating whether options are substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without exercising the options, the cost to exercise the options relative to the total upfront consideration, and the additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options.

        For right-to-test agreements where the options to secure development and commercialization licenses to our ADC technology are considered substantive, we do not consider the development and commercialization licenses to be a deliverable at the inception of the agreement. For those right-to-test agreements entered into prior to the adoption of ASU No. 2009-13 where the options to secure a development and commercialization license are considered substantive, we have deferred the upfront payments received and recognize this revenue over the period during which the collaborator could elect to take options for development and commercialization licenses. These periods are specific to each collaboration agreement. If a collaborator takes an option to acquire a development and commercialization license under these agreements, any substantive option fee is deferred and recognized over the life of the option, generally 12 to 18 months. If a collaborator exercises an option and takes a development and commercialization license to a specific target, we attribute the exercise fee to the development and commercialization license. Upon exercise of an option to acquire a development and commercialization license, we would also attribute any remaining deferred option fee to the development and commercialization license and apply the multiple-element revenue recognition criteria to the development and commercialization license and any other deliverables to determine the appropriate revenue recognition, which will be consistent with our accounting policy for upfront payments on single-target licenses. In the event a right-to-test agreement were to be terminated, we would recognize as revenue any portion of the upfront fee that had not previously been recorded as revenue, but was classified as deferred revenue, at the date of such termination. None of our right-to-test agreements entered into subsequent to the adoption of ASU No. 2009-13 has been determined to contain substantive options.

        For right-to-test agreements where the options to secure development and commercialization licenses to our ADC technology are not considered substantive, we consider the development and commercialization license to be a deliverable at the inception of the agreement and apply the multiple-element revenue recognition criteria to determine the appropriate revenue recognition. None of our right-to-test agreements entered into prior to the adoption of ASU No. 2009-13 has been determined to contain non-substantive options.

        We do not directly control when or if any collaborator will exercise its options for development and commercialization licenses. As a result, we cannot predict when or if we will recognize revenues in connection with any of the foregoing.

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Inventory

        We review our estimates of the net realizable value of our inventory at each reporting period. Our estimate of the net realizable value of our inventory is subject to judgment and estimation. The actual net realizable value of our inventory could vary significantly from our estimates. We consider quantities of raw materials in excess of twelve-month projected usage that are not supported by firm, fixed collaborator orders and projections at the time of the assessment to be excess. During fiscal years 2015, 2014 and 2013, we obtained additional quantities of DMx from our supplier which amounted to more material than would be required by our collaborators over the next twelve months and as a result, we recorded $1.0 million, $364,000 and $798,000, respectively, of charges to research and development expense related to raw material inventory identified as excess. Our collaborators' estimates of their clinical material requirements are based upon expectations of their clinical trials, including the timing, size, dosing schedule and the maximum tolerated dose likely to be reached for the compound being evaluated. Our collaborators' actual requirements for clinical materials may vary significantly from their projections. Significant differences between our collaborators' actual manufacturing orders and their projections could result in our actual twelve- month usage of raw materials varying significantly from our estimated usage at an earlier reporting period. Such differences and/or reductions in collaborators' projections could indicate that we have excess raw material inventory and we would then evaluate the need to record write-downs, which would be included as charges to research and development expense.

Stock-based Compensation

        As of June 30, 2015, we are authorized to grant future awards under one share-based compensation plan, which is the ImmunoGen, Inc. 2006 Employee, Director and Consultant Equity Incentive Plan. The stock-based awards are accounted for under ASC Topic 718, "Compensation—Stock Compensation," pursuant to which the estimated grant date fair value of awards is charged to the statement of operations over the requisite service period, which is the vesting period. Such amounts have been reduced by our estimate of forfeitures for unvested awards.

        The fair value of each stock option is estimated on the date of grant using the Black-Scholes option-pricing model. Expected volatility is based exclusively on historical volatility data of our stock. The expected term of stock options granted is based exclusively on historical data and represents the period of time that stock options granted are expected to be outstanding. The expected term is calculated for and applied to one group of stock options as we do not expect substantially different exercise or post-vesting termination behavior amongst our employee population. The risk-free rate of the stock options is based on the U.S. Treasury rate in effect at the time of grant for the expected term of the stock options. Estimated forfeitures are based on historical data as well as current trends. Stock compensation cost incurred during the years ended June 30, 2015, 2014 and 2013 was $15.3 million, $15.6 million and $12.4 million, respectively.

        Future stock-based compensation may significantly differ based on changes in the fair value of our common stock and our estimates of expected volatility and the other relevant assumptions.

Results of Operations

Revenues

        Our total revenues for the year ended June 30, 2015 were $85.5 million compared with $59.9 million and $35.5 million for the years ended June 30, 2014 and 2013, respectively. The $25.6 and $24.4 million increases in revenues in fiscal year 2015 and fiscal 2014, respectively, are attributable to an increase in license and milestone fees, royalty revenue, non-cash royalty revenue and clinical materials revenue, partially offset by a decrease in research and development support revenue, all of which are discussed below.

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        Revenue from license and milestone fees for the year ended June 30, 2015 increased approximately $18.3 million to $57.8 million from $39.5 million in the year ended June 30, 2014. Revenue from license and milestone fees for the year ended June 30, 2013 was $24.2 million. Included in license and milestone fees for the year ended June 30, 2015 is $15.6 million of license revenue earned upon the execution of two development and commercialization licenses by Lilly, $25.7 million of license revenue earned upon the execution of three development and commercialization licenses by Novartis, two $5 million development milestones achieved under our collaboration agreement with Novartis and $4 million in development milestones achieved under our collaboration agreement with Sanofi. Also, during the current year, we made a change in estimate to our period of substantial involvement as it relates to an exclusive license with Sanofi which resulted in an increase to license and milestone fees of $1.5 million for the current year compared to amounts that would have been recognized pursuant to the Company's previous estimate. Additionally, during the current period, Janssen Biotech terminated its exclusive development and commercialization license with us, and as a result, we recognized the remaining $241,000 of the $1 million upfront fee received upon execution of the license which had been previously deferred. Included in license and milestone fees for the year ended June 30, 2014 is $7.8 million of license revenue earned upon the execution of a development and commercialization license by Lilly, two $5 million regulatory milestones achieved under our collaboration agreement with Roche, $18.2 million of license revenue earned upon the execution of two development and commercialization licenses and a one-year extension of the original term of the multi-target agreement by Novartis, and $2.2 million of revenue from Amgen related to a modification of an existing arrangement. Included in license and milestone fees for the year ended June 30, 2013 was a $10.5 million regulatory milestone achieved under our collaboration agreement with Roche, a $500,000 development milestone achieved under our collaboration agreement with Sanofi and $11.1 million of license revenue earned upon the execution of a development and commercialization license by Novartis. The amount of license and milestone fees we earn is directly related to the number of our collaborators, the collaborators' advancement of the product candidates, and the overall success in the clinical trials of the product candidates. As such, the amount of license and milestone fees may vary widely from quarter to quarter and year to year. Total revenue recognized from license and milestone fees from each of our collaborative partners in the years ended June 30, 2015, 2014 and 2013 is included in the following table (in thousands):

        Deferred revenue of $41.2 million at June 30, 2015 represents payments received from our collaborators pursuant to our license agreements which we have yet to earn pursuant to our revenue recognition policy. Included within this amount is a $20 million upfront payment received from Takeda during fiscal 2015 and $13 million of non-cash consideration recorded in connection with our arrangement with CytomX during fiscal 2014.

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        In February 2013, the US FDA granted marketing approval to Kadcyla, an ADC product resulting from one of our development and commercialization licenses with Roche, through its Genentech unit. We receive royalty reports and payments related to sales of Kadcyla from Roche one quarter in arrears. In accordance with our revenue recognition policy, $13.9 million of royalties on net sales of Kadcyla for the nine-month period ended December 31, 2014 were recorded and included in royalty revenue for the year ended June 30, 2015 and $10.3 million of royalties on net sales of Kadcyla for the twelve-month period ended March 31, 2014 is included in royalty revenue for the year ended June 30, 2014. We recorded $592,000 of royalties on net sales of Kadcyla for the three-month period ended March 31, 2013 in our fourth quarter of fiscal 2013. Total revenues for the year ended June 30, 2015 also include $5.5 million of non-cash royalty revenue on net sales of Kadcyla for the three-month period ended March 31, 2015 as royalties on Kadcyla sales occurring after January 1, 2015 are covered by a royalty purchase agreement whereby the associated cash is remitted to Immunity Royalty Holdings, L.P. See further details regarding royalty obligation in Note E of the Consolidated Financial Statements. We expect royalty revenue to increase in future periods as the underlying net sales of Kadcyla increase.

        Research and development support revenue was $2.8 million for the year ended June 30, 2015, $7.2 million for the year ended June 30, 2014, and $7.9 million for the year ended June 30, 2013. These amounts primarily represent research funding earned based on actual resources utilized under our agreements with our collaborators as shown in the table below. Also included in research and development support revenue are fees for developing antibody-specific conjugation processes on behalf of our collaborators and potential collaborators during the early evaluation and preclinical testing stages of drug development. The amount of research and development support revenue we earn is directly related to the number of our collaborators and potential collaborators, the stage of development of our collaborators' product candidates and the resources our collaborators allocate to the development effort. As such, the amount of development fees may vary widely from quarter to quarter and year to year. Total revenue recognized from research and development support from each of our collaborative partners in the years ended June 30, 2015, 2014 and 2013 is included in the following table (in thousands):

        Clinical materials revenue increased by approximately $2.6 million to $5.5 million in the year ended June 30, 2015 compared to $2.9 million in the year ended June 30, 2014. We earned clinical materials revenue of $2.8 million during the year ended June 30, 2013. During the years ended June 30, 2015, 2014 and 2013, we shipped clinical materials in support of a number of our collaborators' clinical trials, as well as preclinical materials in support of certain collaborators' development efforts and DMx shipments to certain collaborators in support of development and manufacturing efforts. We are compensated at negotiated prices which are generally consistent with what other third-parties would charge. The amount of clinical materials revenue we earn, and the related cost of clinical materials charged to research and development expense, is directly related to the number of clinical trials our collaborators who use us to manufacture clinical materials are preparing or have underway, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period, if any,

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during which patients in the trial receive clinical benefit from the clinical materials, and the demand our collaborators have for clinical-grade material for process development and analytical purposes. As such, the amount of clinical materials revenue and the related cost of clinical materials charged to research and development expense may vary significantly from quarter to quarter and year to year.

Research and Development Expenses

        Our research and development expenses relate to (i) research to evaluate new targets and to develop and evaluate new antibodies, linkers and cytotoxic agents, (ii) preclinical testing of our own and, in certain instances, our collaborators' product candidates, and the cost of our own clinical trials, (iii) development related to clinical and commercial manufacturing processes and (iv) manufacturing operations which also includes raw materials. Our research and development efforts have been primarily focused in the following areas:

•

evaluation of potential antigen targets;



•

evaluation of internally developed and/or in-licensed product candidates and technologies;



•

development and evaluation of additional cytotoxic agents and linkers;



•

activities related to the process, preclinical and clinical development of our internal product candidates;



•

process improvements to our ADC technology;



•

process improvements related to the production of DGN462;



•

process improvements related to the production of DM1, DM4 and strain development of their precursor, ansamitocin P3;



•

operation and maintenance of our conjugate manufacturing facility, including production of our own and our collaborators' clinical materials;



•

production costs for the supply of clinical material for our internal product candidates, including antibody supply, conjugation services and fill/finish services;



•

production costs for the supply of DGN462 and DMx for our and our partners' preclinical and clinical activities;



•

non-pivotal and pivotal development activities with contract manufacturers for conjugation, fill/finish services and the antibody component of our internal product candidates, linkers, and DM1, DM4 and their precursor, ansamitocin P3; and



•

activities pursuant to our development and license agreements with various collaborators.

        Research and development expense for the year ended June 30, 2015 increased $4.8 million to $111.8 million from $107.0 million for the year ended June 30, 2014. Research and development expense was $87.1 million for the year ended June 30, 2013. During the year ended June 30, 2014, we recorded a $12.8 million non-cash charge to research and development expense for technology rights obtained under the collaboration agreement executed with CytomX in January 2014. We had no such charge in fiscal year 2015. Offsetting this decrease were the following increases in expense in fiscal 2015: (i) increased third-party costs related to the advancement of our internal products; (ii) an increase in cost of clinical materials revenue due to timing of orders of such clinical materials from our partners; (iii) an increase in facility-related expenses due primarily to additional laboratory and office space occupied since July 2014 and increased depreciation and amortization related to major capital equipment and improvements; and (iv) salaries and related expenses increased due primarily to increases in personnel and incentive compensation. Research and development salaries and related expenses increased by $5.0 million to $52.6 million in the year ended June 30, 2015 compared to the

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year ended June 30, 2014 and increased by $8.3 million in the year ended June 30, 2014 compared to the year ended June 30, 2013. The average number of our research personnel increased to 266 for the year ended June 30, 2015 compared to 250 for the year ended June 30, 2014. We had an average of 226 for the year ended June 30, 2013. Included in salaries and related expenses for the year ended June 30, 2015 is $9.9 million of stock compensation costs compared to $10.3 million and $7.3 million of stock compensation costs for fiscal years 2014 and 2013, respectively. The higher stock compensation costs in fiscal years 2015 and 2014 compared to fiscal year 2013 are driven by increases in the number of annual options granted due to increases in personnel, as well as higher stock prices in fiscal 2014.

        We are unable to accurately estimate which potential product candidates, if any, will eventually move into our internal preclinical research program. We are unable to reliably estimate the costs to develop these products as a result of the uncertainties related to discovery research efforts as well as preclinical and clinical testing. Our decision to move a product candidate into the clinical development phase is predicated upon the results of preclinical tests. We cannot accurately predict which, if any, of the discovery stage product candidates will advance from preclinical testing and move into our internal clinical development program. The clinical trial and regulatory approval processes for our product candidates that have advanced or that we intend to advance to clinical testing are lengthy, expensive and uncertain in both timing and outcome. As a result, the pace and timing of the clinical development of our product candidates is highly uncertain and may not ever result in approved products. Completion dates and development costs will vary significantly for each product candidate and are difficult to predict. A variety of factors, many of which are outside our control, could cause or contribute to the prevention or delay of the successful completion of our clinical trials, or delay or prevent our obtaining necessary regulatory approvals. The costs to take a product through clinical trials are dependent upon, among other factors, the clinical indications, the timing, size and design of each clinical trial, the number of patients enrolled in each trial, and the speed at which patients are enrolled and treated. Product candidates may be found to be ineffective or to cause unacceptable side effects during clinical trials, may take longer to progress through clinical trials than anticipated, may fail to receive necessary regulatory approvals or may prove impractical to manufacture in commercial quantities at reasonable cost or with acceptable quality.

        The lengthy process of securing FDA approvals for new drugs requires the expenditure of substantial resources. Any failure by us to obtain, or any delay in obtaining, regulatory approvals, would materially adversely affect our product development efforts and our business overall. Accordingly, we cannot currently estimate, with any degree of certainty, the amount of time or money that we will be required to expend in the future on our product candidates prior to their regulatory approval, if such approval is ever granted. As a result of these uncertainties surrounding the timing and outcome of our clinical trials, we are currently unable to estimate when, if ever, our product candidates that have advanced into clinical testing will generate revenues and cash flows.

        We do not track our research and development costs by project. Since we use our research and development resources across multiple research and development projects, we manage our research and development expenses within each of the categories listed in the following table and described in more detail below (in thousands):

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        Research—Research includes expenses associated with activities to evaluate new targets and to develop and evaluate new antibodies, linkers and cytotoxic agents for our products and in support of our collaborators. Such expenses primarily include personnel, fees to in-license certain technology, facilities and lab supplies. Research expenses decreased $10.1 million to $20.7 million in fiscal year 2015 from fiscal year 2014 and increased $13.3 million to $30.8 million in fiscal year 2014 from fiscal year 2013. This decrease in fiscal year 2015 was principally due to a $12.8 million non-cash charge recorded for technology rights obtained under the collaboration agreement executed with CytomX in January 2014, partially offset by an increase in salaries and related expenses and an increase in facility-related expenses. The increase in fiscal 2014 from fiscal 2013 was principally due to the $12.8 million non-cash charge noted above, and to a lesser extent, an increase in salaries and related expenses.

        Preclinical and Clinical Testing—Preclinical and clinical testing includes expenses related to preclinical testing of our own and, in certain instances, our collaborators' product candidates, regulatory activities, and the cost of our own clinical trials. Such expenses include personnel, patient enrollment at our clinical testing sites, consultant fees, contract services, and facility expenses. Preclinical and clinical testing expenses increased $7.9 million to $42.5 million in fiscal year 2015 from fiscal year 2014 and $6.8 million to $34.6 million in fiscal year 2014 from fiscal year 2013. The increase in fiscal year 2015 was principally the result of an increase in contract service expense driven primarily by increased study activities related to mirvetuximab soravtansine and IMGN289, and to a lesser extent, higher salaries and related expenses and an increase in facility-related expenses. Partially offsetting these increases, clinical trial costs decreased marginally due primarily to decreased costs incurred related to the IMGN901 007 study, partially offset by increased costs related to the mirvetuximab soravtansine and IMGN529 studies during the current year. The increase in fiscal year 2014 was principally the result of higher salaries and related expenses driven by an increase in personnel and higher stock compensation costs.

        Process and Product Development—Process and product development expenses include costs for development of clinical and commercial manufacturing processes for our own and collaborator compounds. Such expenses include the costs of personnel, contract services and facility expenses. Total development expenses increased $172,000 to $8.5 million in fiscal year 2015 from fiscal year 2014 and expenses increased $519,000 to $8.3 million in fiscal year 2014 from fiscal year 2013. The increase in fiscal year 2015 was primarily the result of an increase in facility-related expenses. The increase in fiscal year 2014 was primarily the result of an increase in salaries and related expenses, as well as an increase in contract service expense in fiscal 2014 driven primarily by development activities for IMGN779.

        Manufacturing Operations—Manufacturing operations expense includes costs to manufacture preclinical and clinical materials for our own and our collaborators' product candidates, quality control and quality assurance activities and costs to support the operation and maintenance of our conjugate manufacturing facility. Such expenses include personnel, raw materials for our and our collaborators' preclinical studies and clinical trials, non-pivotal and pivotal development costs with contract manufacturing organizations, manufacturing supplies, and facilities expense. Manufacturing operations expense increased $6.7 million to $40.0 million in fiscal year 2015 from fiscal year 2014 and decreased $644,000 to $33.3 million in fiscal year 2014 from fiscal year 2013. The increase in fiscal year 2015 was primarily the result of i) an increase in cost of clinical materials revenue charged to research and development expense due to timing of orders of such clinical materials from our partners; (ii) an increase in contract service expense driven by increased third-party conjugation activities to prepare for commercial-scale and increased cytotoxic agent activities; (iii) an increase in antibody development and supply expense driven primarily by commercial-ready activities for mirvetuximab soravtansine; and (iv) an increase in salaries and related expenses driven by increased personnel and increased incentive compensation. The decrease in fiscal year 2014 was primarily the result of (i) a decrease in antibody development and supply expense driven primarily by supply required in fiscal 2013 for our currently discontinued IMGN289 and IMGN901 programs, as well as pivotal activities performed for our

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IMGN901 program, partially offset by non-pivotal activities performed and supply required for our IMGN779 program during fiscal 2014; (ii) a decrease in fill/finish costs due primarily to costs to transfer our internal programs to a new supplier during fiscal 2013; and (iii) an increase in costs capitalized into inventory due to a greater number of manufactured batches of conjugated materials on behalf of our collaborators. Partially offsetting these cost decreases, salaries and related expenses increased during fiscal 2014 and contract service expense increased due primarily to increased study activities related to our cytotoxic agents.

        Antibody development and supply expense in anticipation of potential future clinical trials, as well as our ongoing trials, was $8.8 million in fiscal year 2015, $7.2 million in fiscal year 2014, and $10.8 million in fiscal year 2013. The process of antibody production is lengthy due in part to the lead time to establish a satisfactory production process at a vendor. Accordingly, costs incurred related to antibody production and development have fluctuated from period to period and we expect these cost fluctuations to continue in the future.

        We expect that future research and development expenses will increase, including salaries and related expenses, due to our continuing advancement and support of our internal product candidates through clinical trials.

General and Administrative Expenses

        General and administrative expenses for the year ended June 30, 2015 increased $3.7 million to $28.2 million from $24.5 million for the year ended June 30, 2014. General and administrative expenses for the year ended June 30, 2013 were $21.5 million. The increases in fiscal years 2015 and 2014 were primarily due to increases in salaries and related expenses, as well as increases in professional service fees, particularly consulting fees and patent expenses. We expect general and administrative expenses to increase marginally in fiscal 2016 compared to fiscal 2015 due primarily to increases in salaries and related expenses.

Investment Income, net

        Investment income for the years ended June 30, 2015, 2014 and 2013 was $69,000, $44,000 and $126,000, respectively.

Non-Cash Interest Expense on Liability Related to Sale of Future Royalty

        In April 2015, Immunity Royalty Holdings, L.P. (IRH) purchased our right to receive 100% of the royalty payments on commercial sales of Kadcyla arising under our development and commercialization license with Genentech, until IRH has received aggregate royalties equal to $235 million or $260 million, depending on when the aggregate royalties received by IRH reach a specified milestone. As described in Note E to our Consolidated Financial Statements, this royalty sale transaction has been recorded as a liability that amortizes over the estimated royalty payment period as Kadcyla royalties are remitted directly to the purchaser. We impute interest on the transaction and record interest expense at the effective interest rate, which we currently estimate to be approximately 10%. There are a number of factors that could materially affect the estimated interest rate, in particular, the amount and timing of royalty payments from future net sales of Kadcyla, and we will assess this estimate on a periodic basis. As a result, future interest rates could differ significantly and any such change in interest rate will be adjusted prospectively.

Other (Expense) Income, net

        Other (expense) income, net for the years ended June 30, 2015, 2014 and 2013 was $(916,000), $123,000 and $72,000, respectively. We incurred $(910,000), $120,000, and $(153,000) in foreign currency exchange (losses) and gains related to obligations with non-U.S. dollar-based suppliers and

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Euro cash balances maintained to fulfill them during the years ended June 30, 2015, 2014 and 2013, respectively, and we recorded net gains on foreign currency forward contracts of $2,000 and $197,000 in fiscal years 2014 and 2013, respectively.

Liquidity and Capital Resources

Cash Flows

        We require cash to fund our operating expenses, including the advancement of our own clinical programs, and to make capital expenditures. Historically, we have funded our cash requirements primarily through equity financings in public markets and payments from our collaborators, including license fees, milestones, research funding and more recently, royalties. As of June 30, 2015, we had approximately $278.1 million in cash and cash equivalents. Net cash used for operating activities was $55.3 million, $53.7 million and $60.3 million during the years ended June 30, 2015, 2014 and 2013, respectively. The principal use of cash in operating activities for all periods presented was to fund our net loss, adjusted for non-cash items. Cash used for operating activities in fiscal 2015 benefited from the $20 million upfront payment received from Takeda in March 2015 with the execution of a right- to-test agreement between the companies.

        Net cash used for investing activities was $7.4 million, $8.2 million and $3.7 million for the years ended June 30, 2015, 2014 and 2013, respectively, and substantially represents cash outflows from capital expenditures. Capital expenditures were $7.4 million, $8.2 million and $3.8 million for the fiscal years ended June 30, 2015, 2014 and 2013, respectively. Capital expenditures for the years ended June 30, 2015, 2014 and 2013 consisted primarily of leasehold improvements to the laboratory and office space at our corporate headquarters and manufacturing facility, laboratory equipment and computer software applications.

        Net cash provided by financing activities was $198.6 million, $9.1 million and $98.0 million for the years ended June 30, 2015, 2014 and 2013, respectively, which includes the proceeds from the exercise of approximately 651,000, 1.1 million and 666,000 stock options, respectively. Also, pursuant to a public offering, in fiscal 2013, we issued and sold 6,250,000 shares of our common stock resulting in net proceeds of $94.0 million.

        As discussed above, in April 2015, Immunity Royalty Holdings, L.P. purchased our right to receive 100% of the royalty payments on commercial sales of Kadcyla. At consummation of the transaction in April 2015, we received gross cash proceeds of $200 million. We recorded these cash proceeds as a deferred royalty obligation liability which is being amortized over the expected royalty recovery period. As part of this transaction, the Company incurred approximately $5.9 million in transaction costs.

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        We anticipate that our current capital resources and expected future collaborator payments under existing collaborations will enable us to meet our operational expenses and capital expenditures through fiscal year 2017. However, we cannot provide assurance that such collaborative agreement funding will, in fact, be received. Should we or our partners not meet some or all of the terms and conditions of our various collaboration agreements, we may be required to pursue additional strategic partners, secure alternative financing arrangements, and/or defer or limit some or all of our research, development and/or clinical projects.

Contractual Obligations

        Below is a table that presents our contractual obligations and commercial commitments as of June 30, 2015 (in thousands):

        In addition to the above table, we are contractually obligated to make future success-based development, regulatory or sales milestone payments in conjunction with certain collaborative agreements. These payments are contingent upon the occurrence of certain future events and, given the nature of these events, it is unclear when, if ever, we may be required to pay such amounts. Therefore, the timing of any future payment is not reasonably estimable. As a result, these contingent payments have not been included in the table above or recorded in our consolidated financial statements.

        As of June 30, 2015, the maximum amount that may be payable in the future under our current collaborative agreements is $162 million, $1.4 million of which is reimbursable by a third party under a separate agreement.

Recent Accounting Pronouncements

        In May 2014, the FASB issued Accounting Standards Update 2014-9, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), to clarify the principles for recognizing revenue. This update provides a comprehensive new revenue recognition model that requires revenue to be recognized in a manner to depict the transfer of goods or services to a customer at an amount that reflects the consideration expected to be received in exchange for those goods or services. The original effective date would have required us to adopt beginning in our first quarter of fiscal 2018. In July 2015, the FASB voted to amend ASU 2014-09 by approving a one-year deferral of the effective date as well as providing the option to early adopt the standard on the original effective date. Accordingly, we may adopt the standard in either our first quarter of fiscal 2018 or 2019. The new revenue standard allows for either full retrospective or modified retrospective application. We are currently evaluating the

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timing of its adoption and the impact that this guidance will have on our consolidated financial statements and related disclosures.

        In August 2014, the FASB issued Accounting Standards Update 2014-15, Presentation of Financial Statements-Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern. This new standard gives a company's management the final responsibilities to decide whether there's substantial doubt about the company's ability to continue as a going concern and to provide related footnote disclosures. The standard provides guidance to management, with principles and definitions that are intended to reduce diversity in the timing and content of disclosures that companies commonly provide in their footnotes. Under the new standard, management must decide whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the company's ability to continue as a going concern within one year after the date that the financial statements are issued, or within one year after the date that the financial statements are available to be issued when applicable. This guidance is effective for annual reporting beginning after December 15, 2016, including interim periods within the year of adoption, with early application permitted. Accordingly, the standard is effective for us on July 1, 2017. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements.

        In April 2015, the FASB issued Accounting Standards Update 2015-03, Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. To simplify presentation of debt issuance costs, this new standard requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this update. This guidance is effective for annual reporting beginning after December 15, 2015, including interim periods within the year of adoption, and calls for retrospective application, with early application permitted. Accordingly, the standard is effective for us on July 1, 2016. We are currently evaluating the impact that this guidance will have on our consolidated financial statements.

        In July 2015, the FASB issued Accounting Standards Update 2015-11, Simplifying the Measurement of Inventory (Topic 330). To simplify the principles for subsequent measurement of inventory, this new standard requires inventory measured using any method other than LIFO or the retail method shall be measured at the lower of cost and net realizable value, rather than lower of cost or market. This guidance is effective for annual reporting beginning after December 15, 2016, including interim periods within the year of adoption, and calls for prospective application, with early application permitted. Accordingly, the standard is effective for us on July 1, 2017. The adoption of this guidance is not expected to have a material impact on our consolidated financial statements.

Off-Balance Sheet Arrangements

        None.

Item 7A.    Quantitative and Qualitative Disclosure About Market Risk

        We maintain an investment portfolio in accordance with our investment policy. The primary objectives of our investment policy are to preserve principal, maintain proper liquidity to meet operating needs and maximize yields. Although our investments are subject to credit risk, our investment policy specifies credit quality standards for our investments and limits the amount of credit exposure from any single issue, issuer or type of investment. Our investments are also subject to interest rate risk and will decrease in value if market interest rates increase. However, due to the conservative nature of our investments and relatively short duration, interest rate risk is mitigated. We do not currently own derivative financial instruments in our investment portfolio. Accordingly, we do

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not believe there is any material market risk exposure with respect to derivative or other financial instruments that would require disclosure under this item.

        Our foreign currency hedging program uses either forward contracts or a Euro-denominated bank account to manage the foreign currency exposures that exist as part of our ongoing business operations. Our foreign currency risk management strategy is principally designed to mitigate the future potential financial impact of changes in the value of transactions, anticipated transactions and balances denominated in foreign currency, resulting from changes in foreign currency exchange rates. Our market risks associated with changes in foreign currency exchange rates are currently limited to a Euro-denominated bank account as we have no forward contracts at June 30, 2015.

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Item 8.    Financial Statements and Supplementary Data

IMMUNOGEN, INC.
INDEX TO CONSOLIDATED FINANCIAL STATEMENTS

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Report of Independent Registered Public Accounting Firm

The Board of Directors and Shareholders of ImmunoGen, Inc.

        We have audited the accompanying consolidated balance sheets of ImmunoGen, Inc. as of June 30, 2015 and 2014, and the related consolidated statements of operations and comprehensive loss, shareholders' equity and cash flows for each of the three years in the period ended June 30, 2015. These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on these financial statements based on our audits.

        We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

        In our opinion, the financial statements referred to above present fairly, in all material respects, the consolidated financial position of ImmunoGen, Inc. at June 30, 2015 and 2014, and the consolidated results of its operations and its cash flows for each of the three years in the period ended June 30, 2015, in conformity with U.S. generally accepted accounting principles.

        We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States), ImmunoGen, Inc.'s internal control over financial reporting as of June 30, 2015, based on criteria established in Internal Control—Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 framework) and our report dated August 27, 2015 expressed an unqualified opinion thereon.

/s/ Ernst & Young LLP

Boston, Massachusetts
August 27, 2015

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IMMUNOGEN, INC.

CONSOLIDATED BALANCE SHEETS

In thousands, except per share amounts