Form 10-K (Part I)

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, 2006 unless otherwise indicated. For a description of the risk factors affecting or applicable to our business, see "Risk Factors," below.

The Company

We develop novel, targeted therapeutics for the treatment of cancer using our expertise in cancer biology, monoclonal antibodies (antibodies), and small molecule cell-killing (cytotoxic) agents. Our Tumor-Activated Prodrug (TAP) technology uses antibodies to deliver a potent cytotoxic agent specifically to cancer cells. Our TAP technology is designed to enable the creation of highly effective, well-tolerated anticancer products.

We believe that our TAP technology and our expertise in antibodies will enable us to become a leader in the application of antibodies for the treatment of cancer. We plan to achieve this goal through the development of our own anticancer products and through outlicenses of our TAP technology to other companies. These outlicenses are designed to expand the number of anticancer therapeutics developed that can provide us a financial return by enabling the creation of TAP compounds with antibodies proprietary to other companies and therefore not available for our own product programs. Our collaborative partners include: Amgen Inc. (formerly Abgenix, Inc.); Biogen Idec, Inc.; Boehringer Ingelheim International GmbH; Centocor, Inc. (a wholly owned subsidiary of Johnson & Johnson); Genentech, Inc.; Millennium Pharmaceuticals, Inc.; the sanofi-aventis Group; and effective July 7, 2006, Biotest AG. We also have a broader collaboration with sanofi-aventis.

We believe that the key initiatives to successfully carry out our business plan are:

We were organized as a Massachusetts corporation in March 1981. Our principal offices are located at 128 Sidney Street, Cambridge, Massachusetts 02139, and our telephone number is (617) 995-2500. We maintain a web site at www.ImmunoGen.com , where certain information about us is available. Please note that the 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 Relations" section of our website as soon as reasonably practicable after those materials have been electronically filed with, or furnished to, the Securities and Exchange Commission. We have adopted a Code of Corporate Conduct that applies to all our directors, officers and employees and a 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 Investor Relations section of our website.

Our TAP Technology

Traditional chemotherapeutics typically kill healthy cells as well as cancerous cells, which can limit their ability to be dosed to full potential and result in significant side effects. Antibodies, in contrast, can be created that bind specifically to targets found on cancer cells, thereby allowing them to selectively attach to these cells. However, many of the antibodies that have been created to bind specifically to targets found on cancer cells have been found to have little, if any, impact on a cancer cell once bound to it. Our TAP technology uses tumor-targeting antibodies to deliver a potent cell-killing agent specifically to cancer cells in order to kill these cells with minimal damage to healthy tissue. This technology can be used to create potent anticancer therapeutics with antibodies that are unlikely to otherwise become commercial products.

The cell-killing agents we attach to antibodies were developed specifically for antibody-directed delivery to cancer cells and have the following features:

We have developed alternative cell-killing agents (such as DM1 and DM4) and alternative means of their attachment to antibodies (such as highly-hindered disulfide bond, less-hindered disulfide bond, thioether bond) as we and our collaborators have found that the best design for each TAP compound varies depending upon the antibody and its target. These innovations are reflected in TAP compounds now in clinical testing.

In addition to our TAP technology, we have established expertise in the development and humanization of antibodies and in cancer biology. Our manufacturing facility in Norwood, MA, helps us and our collaborators rapidly advance new TAP compounds into human trials by enabling the production of the drug supplies needed for initial clinical testing. Our Norwood facility has four manufacturing suites and all of the functions needed to make TAP compounds in compliance with the current Good Manufacturing Practice, or cGMP, as provided by the United States Food and Drug Administration. We use this expertise together with our TAP technology to develop TAP compounds. We also use this expertise to develop "naked" (non-immunoconjugate) antibody compounds. For example, we developed the anti-IGF-1R naked antibody now in development by sanofi-aventis as AVE1642.

Product Candidates

The following table summarizes the antigen target, cancer(s) expressing the target, and development stage for compounds in development by us and our collaborators. The results from preclinical testing and early clinical trials may not be predictive of results obtained in subsequent clinical trials and there can be no assurance that our or our collaborators' clinical trials will demonstrate the level of safety and efficacy of any product candidates necessary to obtain regulatory approval.

Product Candidate		Antigen Target		Cancer(s) expressing target		Development Stage(1)		Collaborative Partner
HuN901-DM1		CD56		Small-cell lung cancer; certain neuroendocrine cancers; certain hematological malignancies		Phase I and Phase II		Proprietary to ImmunoGen
HuC242-DM4		CanAg		Gastrointestinal cancers, including colorectal, pancreatic, and gastric cancers; many non-small-cell lung cancers		Phase I		Proprietary to ImmunoGen
AVE9633		CD33		Acute myeloid leukemia		Phase I		sanofi-aventis
Trastuzumab-DM1		HER2		HER2-positive metastatic breast cancers		Phase I		Genentech
AVE1642		IGF-1R		Solid tumors and certain hematological malignancies		Research/preclinical		sanofi-aventis
SAR3419		CD19		B-cell malignancies including non-Hodgkin’s lymphoma		Research/ preclinical		sanofi-aventis
TAP compound		Cripto		Solid tumors		Research/ preclinical		Biogen Idec
TAP compound		av integrin		Multiple tumor types		Research/ preclinical		Centocor
TAP compound		On multiple myeloma		Multiple myeloma, other		Research/preclinical		Biotest AG *
TAP compounds		Undisclosed		Undisclosed		Research/preclinical		Genentech
Others		Undisclosed		Undisclosed		Research/preclinical		ImmunoGen, Partners

HuN901-DM1

We are developing the TAP compound, huN901-DM1, for the treatment of CD56-expressing cancers. These include small-cell lung cancer (SCLC), other cancers of neuroendocrine origin, and many cases of multiple myeloma as well as other hematological malignancies. This product candidate consists of our huN901 antibody, which binds to CD56, with our DM1 attached as the cell-killing agent.

We have three clinical trials underway with huN901-DM1. Study 001 is evaluating the compound when dosed weekly for four weeks every six weeks. This study was started by our former partner, British Biotech (now Vernalis), and assumed by us on July 1, 2004. The Phase II segment of this study that is underway evaluates huN901-DM1 when given at the maximum tolerated dose (MTD), as established in the Phase I segment of the study, to patients with relapsed SCLC. Objective evidence of anticancer activity was reported among the initial 14 patients treated, prompting the expansion of this leg of the study to include 35 patients. Patient enrollment is underway at multiple clinical centers in the United States. Study 002 also was started by British Biotech and was assumed by us in December 2005. This study evaluates huN901-DM1 in the treatment of solid tumors such as SCLC, but in Study 002 the compound is dosed daily for three days in a 21-day cycle. Interim data from this study were reported at the American Association for Cancer Research (AACR), the U.S. National Cancer Institute (NCI) and the European Organisation for Research and Treatment of Cancer (EORTC), or the AACR-NCI-EORTC, meeting in November 2005 and included objective evidence of antitumor activity. We expect to report additional findings from this study within the next twelve months.

In Study 003, huN901-DM1 is being evaluated in the treatment of the hematological or "liquid" tumor malignancy, multiple myeloma. Approximately 70% of multiple myeloma cases express CD56. We expect to report data from this study within the next twelve months. We are evaluating additional development opportunities for this compound.

HuC242-DM4

Our TAP product candidate, huC242-DM4, consists of the humanized antibody, huC242, with our DM4 cell-killing agent attached. HuC242 binds to the CanAg receptor found on colorectal, pancreatic, and other gastrointestinal tumors and on many non-small-cell lung cancers.

This compound is in Phase I clinical testing for the treatment of CanAg-expressing cancers. In this dose-escalation study, huC242-DM4 is administered every three weeks to patients with refractory CanAgexpressing cancers. The primary objective of this study is to evaluate the safety and pharmacokinetics of huC242-DM4 and to identify its MTD with this dosing schedule. Once the MTD is defined, additional patients will be enrolled with tumors that consistently and intensely express CanAg to gain further experience with the compound in that patient population. We expect to report data from this study and to complete patient enrollment in it within the next twelve months.

An earlier version of this compound, huC242-DM1, was found to be well tolerated in initial clinical testing and to demonstrate evidence of anticancer activity. Based on our preclinical studies, we expect huC242-DM4 to be more effective than huC242-DM1 with a comparable tolerability profile.

AVE9633

This TAP compound was developed by us and licensed to sanofi-aventis from our preclinical pipeline as part of a broader collaboration. It comprises our huMy9-6 antibody, which targets CD33, and our DM4 cell-killing agent. On March 16, 2005, sanofi-aventis informed us that patient dosing with AVE9633 had begun, triggering a $2 million milestone payment to us. This compound is in clinical testing in the United States and Europe for the treatment of acute myeloid leukemia.

Trastuzumab-DM1

Genentech developed this TAP compound under a 2000 license that grants Genentech the exclusive right to use our maytansinoid TAP technology (such as DM1 and DM4) with antibodies to HER2 including trastuzumab (Herceptin®). On January 27, 2006, Genentech informed us that the Investigational New Drug (IND) application for trastuzumab-DM1 had become effective, triggering a $2 million 8 milestone payment to us. Phase I evaluation of trastuzumab-DM1 is underway in patients with HER2-expressing metastatic breast cancer.

Herceptin® is a registered trademark of Genentech.

AVE1642

This naked antibody compound was developed by ImmunoGen and licensed to sanofi-aventis from our preclinical pipeline as part of our broader collaboration with sanofi-aventis. AVE1642 binds to and blocks IGF-1R and has potential utility in the treatment of certain solid tumors and hematological malignancies.

SAR3419

Sanofi-aventis also licensed this TAP compound from our preclinical pipeline as part of our broader collaboration. SAR3419 targets CD19, which is associated with certain B-cell malignancies, including non- Hodgkin's lymphoma, and is in preclinical development.

Cripto-targeting TAP compound

This TAP compound is in development by Biogen Idec under a 2004 license that grants Biogen Idec the exclusive right to use our maytansinoid TAP technology with antibodies to the tumor cell target Cripto.

av integrin-targeting TAP compound

This TAP compound is in development by Centocor under the 2004 license that grants Centocor the exclusive right to use our maytansinoid TAP technology with antibodies to the cancer target αv integrin.

Biotest TAP compound*

This TAP compound is in development by Biotest AG under the 2006 license that grants Biotest the exclusive right to use our maytansinoid TAP technology with antibodies to a specific target found on multiple myeloma and certain other cancers.
_____________________________
(*) effective July 7, 2006

Other Compounds in Development

Additional undisclosed product candidates are in development internally and through our collaborations with sanofi-aventis, Genentech and others.

MLN2704

In February 2002, Millennium licensed the exclusive right to use our TAP technology with antibodies to the Prostate-Specific Membrane Antigen (PSMA). In November 2002, Millennium initiated clinical testing with MLN2704, a TAP compound comprising our DM1 cell-killing agent and the PSMA-targeting J591 antibody licensed by Millennium from BZL Biologics. In 2004, 2005, and 2006, findings from two early-stage clinical trials with MLN2704 were reported at the annual meeting of the American Society of Clinical Oncology. During 2005, Millennium disclosed that the company expected to make a "next step" decision for MLN2704 by year end. In early January 2006, Millennium disclosed that there were concerns related to the economics and therapeutic window of the compound, and in late January 2006, Millennium announced that the company was discontinuing further development of MLN2704. Millennium retains the Company's exclusive right to use our TAP technology with antibodies to PSMA.

Bivatuzumab mertansine

In November 2001, Boehringer Ingelheim licensed the exclusive right to use our DM1 TAP technology with antibodies that target CD44. In late 2002, Boehringer Ingelheim advanced into clinical testing a TAP compound, bivatuzumab mertansine, consisting of their anti-CD44v6 antibody and our DM1. On February 7, 2005, Boehringer Ingelheim informed us that they had elected to discontinue development of bivatuzumab mertansine due to the occurrence of skin toxicity in early clinical testing in patients with advanced carcinoma. Published data indicate that CD44v6 is expressed on normal proliferating epidermal skin cells as well as on various carcinomas. Boehringer Ingelheim has exercised its option to substitute a different target in the agreement with us.

Our Market Opportunity

Cancer remains a leading cause of death worldwide and the second leading cause of death in the United States The American Cancer Society (ACS) estimates that 565,000 people will die from cancer in the United States in 2006. The ACS also projects that 1.4 million people in the United States will be diagnosed with cancer this year. Because cancer is a progressive disease, the total number of people living with cancer significantly exceeds the number of patients diagnosed with cancer in a given year.

Targeted anticancer therapies offer potential advantages in efficacy and tolerability over traditional chemotherapeutic agents. At the same time, their potential market is limited to those cancers that express their target. In recent years, several targeted anticancer therapies have enjoyed considerable commercial success. These include rituximab (Rituxan®), an antibody that targets the CD20 antigen associated with certain B-cell malignancies, and trastuzumab (Herceptin®), an antibody that targets HER2 expression associated with certain breast cancers.

The potential market for anticancer drugs exceeds the number of patients treated with anticancer drugs as many types of cancer are typically treated with multiple agents at the same time. Additionally, patients often receive multiple drug regimens sequentially, either to treat recurrence of the disease or to help prevent recurrence of the disease.

Out-Licenses and Collaborations

As part of our business strategy to develop and commercialize TAP compounds, we enter into license agreements with third parties where we grant them the right to use our TAP technology with their proprietary antibodies. In some cases, we have out-licensed certain rights to our own TAP compounds to companies with product development and commercialization capabilities that we desired to access. In exchange, we are entitled to receive upfront fees, potential milestone payments and royalties on any product sales. Our principal out-licenses and collaborative agreements are described below.

sanofi-aventis ( formerly Aventis)

In July 2003, we entered into a broad collaboration agreement with Aventis (now sanofi-aventis) to discover, develop and commercialize anticancer therapeutics. The agreement provides sanofi-aventis with worldwide commercialization rights to new product candidates created through the collaboration as well as worldwide development and commercialization rights to three product candidates from our preclinical pipeline: our anti-CD33 TAP compound (AVE9633) for acute myeloid leukemia, our anti-IGF-1R antibody (AVE1642) for multiple cancers and our anti-CD19 TAP compound (SAR3419) for certain B-cell malignancies. The overall term of the agreement extends to the later of the latest patent to expire or 12 years after the latest launch of any product discovered, developed and/or commercialized under the agreement. The agreement provides that we will receive a minimum of $50.7 million of committed research funding during a three-year research period that began September 1, 2003, of which a substantial portion has been received as of June 30, 2006.

Under the 2003 agreement, sanofi-aventis has the option, upon giving 12 months' advance notice for each, to request that we extend the research program for two additional 12-month periods. The collaboration agreement also provides for certain other payments based on the achievement of product candidate milestones and royalties on sales of any resulting products, if and when such sales commence. Assuming all benchmarks are met, we will receive milestone payments of between $21.5 million and $30.0 million per antigen target. In August 2005, sanofi-aventis exercised its contractual right to extend the term of its research program with us and committed to fund $18.2 million in research and support over the 12 month period following September 1, 2006. This funding is in addition to the research and support already committed for the three years ending August 31, 2006. Sanofi-aventis must notify us no later than August 31, 2006 if they intend to extend the research program for the second additional 12-month period that begins in September 2007. Should they elect to exercise its contractual right to extend the term of the research program for the second additional 12-month period, we will receive additional research funding.

The sanofi-aventis collaboration agreement provides us an option to certain co-promotion rights in the United States on a product-by-product basis. Sanofi-aventis is responsible for the cost of the development, manufacturing and marketing of any products created through the collaboration. We are reimbursed for any preclinical and clinical materials that we make under the agreement.

The terms of our collaboration agreement with sanofi-aventis place certain restrictions upon us. Subject to pre-existing obligations under our other collaboration agreements that were in effect at the time we signed the collaboration agreement with sanofi-aventis, (i) we may only enter into a specified number of additional single target collaboration agreements during the term of the collaborative research program, (ii) during the term of the collaborative research program and for a specified period thereafter, we are prohibited from entering into any single target license, other than with sanofi-aventis, related to use of our TAP technology with any taxane effector molecule, and (iii) during the course of the collaborative research program, we are obligated to propose to sanofi-aventis promising targets for antibody-based anticancer agents up to a defined maximum number of targets. These targets can lead to the creation of new collaboration products that potentially can be an additional source of milestone payments and royalties to us. Whether or not sanofi-aventis elects to pursue development of compounds to these targets depends on factors that include perceived commercial opportunity, compatibility with other sanofi-aventis programs, internal business policies, and the number of targets already accepted.

Additionally, the terms of the collaboration agreement allow sanofi-aventis to terminate our participation in the research program and/or our co-promotion rights if there were a change of control of the Company.

Biogen Idec, Inc.

On October 1, 2004, we entered into a development and license agreement with Biogen Idec, Inc. Under the terms of the agreement, Biogen Idec received exclusive worldwide rights to develop and commercialize anticancer therapeutics using antibodies to the tumor cell target Cripto and a maytansinoid cell-killing agent developed by us. Biogen Idec is responsible for the research, development, manufacturing, and marketing of any products resulting from the license. Under the terms of the agreement, we received from Biogen Idec an upfront payment of $1.0 million upon execution of the agreement. This upfront amount is subject to credit, as defined under the agreement, if Biogen Idec does not submit certain regulatory filings by June 30, 2008. Assuming all benchmarks are met, we could receive up to $42.0 million in milestone payments under this agreement. We will also receive compensation from Biogen Idec for product development research done on its behalf, as well as for the production of preclinical and clinical materials.

Biotest AG

Subsequent to the end of fiscal 2006, on July 7, 2006, we entered into a development and license agreement with Biotest AG. The agreement grants Biotest AG exclusive rights to use our TAP technology with antibodies to a specific target to create anticancer therapeutics. Under the agreement, we received a $1 million upfront payment upon execution of the agreement, and could potentially receive up to $35.5 million in milestone payments, and royalties on the sales of any resulting products. We will receive manufacturing payments for any preclinical and clinical materials made at the request of Biotest. The agreement also provides us with the right to elect to participate, at specific stages during the clinical evaluation of any compound created under this agreement, in the United States development and commercialization of that compound in lieu of receiving royalties on United States sales of that product and milestone payments not yet earned. We can exercise this right by making a payment to Biotest of an agreed-upon fee of $5 million or $15 million, depending on the stage of development. Upon exercise of this right, we would share equally with Biotest the associated costs of product development and commercialization in the United States along with the profit, if any, from United States product sales.

Boehringer Ingelheim International GmbH

In November 2001, we entered into a collaboration agreement with Boehringer Ingelheim that enables Boehringer Ingelheim to develop TAP compounds that combine our TAP technology with antibodies to CD44. Under the terms of the agreement, we received an upfront payment upon commencement of the agreement and could receive, based upon the exchange rate on November 27, 2001, the effective date of the agreement, approximately $41.5 million in potential payments upon Boehringer Ingelheim's achievement of certain milestones in addition to royalty payments on future product sales, if and when such sales commence. In October 2002, Boehringer Ingelheim confirmed with us that clinical testing of the novel anticancer agent, bivatuzumab mertansine, composed of ImmunoGen's DM1 effector molecule and Boehringer Ingelheim's anti-CD44v6 antibody, had commenced on or about September 24, 2002. This event triggered a milestone payment of $1.0 million from Boehringer Ingelheim to us. On February 7, 2005, Boehringer Ingelheim notified us that development of bivatuzumab mertansine had been discontinued. Boehringer Ingelheim retained its right to use our DM1 TAP technology and has exercised its right to create an anticancer compound to a different antigen.

Centocor

On December 23, 2004, we entered into a development and license agreement with Centocor, Inc., a wholly owned subsidiary of Johnson and Johnson. Under the terms of this agreement, Centocor has exclusive worldwide rights to develop and commercialize anticancer therapeutics that comprise an antibody developed by Centocor that binds to the cancer target " v integrin and a maytansinoid cell-killing agent developed by us. Centocor is responsible for the research, development, manufacturing, and marketing of any products resulting from the license. Under the terms of the agreement, we received a non-refundable upfront payment of $1.0 million upon execution of the agreement. In addition to royalties on future product sales, when and if such sales commence, the terms of the agreement include certain other payments upon Centocor's achievement of milestones. Assuming all benchmarks are met, we would receive $42.5 million in milestone payments under this agreement.

Millennium Pharmaceuticals, Inc.

In March 2001, we entered into a five-year collaboration agreement with Millennium upon which we received a non-refundable upfront fee of $2.0 million. Millennium acquired a license to utilize our TAP technology in its antibody product research efforts and an option to obtain product licenses for a restricted number of antigen targets during the collaboration. For each license to an antigen target taken, the collaboration agreement provides for license and milestone payments potentially totaling $41.0 million and royalties on sales of any resulting products, if and when such sales commence. Millennium is responsible for product development, manufacturing and marketing of any resulting products. We are to be reimbursed for any preclinical and clinical materials that we make under the agreement.

Pursuant to this agreement, in February 2002 Millennium licensed the exclusive right to use our maytansinoid technology with antibodies targeting the Prostate-Specific Membrane Antigen (PSMA). In March 2002, we received a license fee from Millennium pursuant to this license agreement. In November 2002, Millennium informed us that clinical testing of MLN2704, comprised of our cytotoxic agent DM1 and Millennium's MLN591 antibody, had been initiated. This event triggered a milestone payment of $1.0 million from Millennium to us. On January 25, 2006, Millennium notified us that, as part of its ongoing portfolio management process and based on the evaluation of recent clinical data in the context of other opportunities in its pipeline, Millennium had decided not to continue the development of its MLN2704 compound. Millennium retains its right to use our maytansinoid TAP technology with antibodies targeting PSMA.

On March 27, 2006, we agreed to amend the 2001 agreement with Millennium, which was scheduled to expire March 30, 2006. The amendment extends the agreement for an additional year which ends March 30, 2007. In consideration for this extension, Millennium paid us an extension fee equal to $250,000.

Amgen, Inc. (formerly Abgenix)

In September 2000, we entered into a collaboration agreement with Abgenix (now Amgen). The agreement provides Amgen with access to our maytansinoid technology for use with their antibodies along with the ability to acquire both exclusive and nonexclusive options to obtain product licenses for antig en targets. Each option has a specified option period during which Amgen may obtain a product license. Under this agreement Amgen has the right to extend each option period by a specified amount of time in exchange for an extension fee. We received a total of $5.0 million in technology access fee payments under this agreement and are entitled to potential milestone payments and royalties on net sales of resulting products, if and when such sales commence. In addition, on September 7, 2000, Abgenix purchased $15.0 million of our common stock in accordance with the agreement. We understand that these shares were sold in fiscal 2006. Our agreement with Amgen will terminate upon expiration of the 10-year term plus any exercised option extension periods during which Amgen has access to our technology.

Vernalis (formerly British Biotech plc)

In August 2003, Vernalis completed its acquisition of British Biotech. In connection with this acquisition, the merged company, called Vernalis plc, announced that it intended to review its merged product candidate portfolio, including its collaboration with ImmunoGen on huN901-DM1. After discussion with Vernalis, in January 2004, we announced that we would take over further development of the product candidate, including the advancement of huN901-DM1 in our own clinical trials. Pursuant to the terms of the termination agreement executed on January 7, 2004, Vernalis, which relinquished its rights to the product, would, at its own expense, complete Study 002 and was responsible for Study 001 through June 30, 2004. On December 15, 2005, we executed an agreement to amend the residual obligation terms of the January 7, 2004 Termination Agreement with Vernalis. Under the terms of the amendment, we assumed responsibility for Study 002 as of December 15, 2005, including the cost of its completion. Under the amendment, Vernalis paid us $365,000 in consideration of the expected cost of the obligations assumed by us under the amendment.

Genentech, Inc.

In May 2000, we entered into two separate agreements with Genentech. The first agreement grants Genentech an exclusive license to our maytansinoid technology for use with antibodies, such as trastuzumab (Herceptin®), that target HER2. Under the terms of this agreement, Genentech has exclusive worldwide rights to develop and commercialize TAP compounds with antibodies that target HER2. Genentech will be responsible for manufacturing, product development and marketing of any products resulting from the agreement; we will be reimbursed for any preclinical and clinical materials that we manufacture under the agreement. We received a $2.0 million non-refundable payment upon execution of the agreement. In addition to royalties on net sales if and when they occur, the terms of the agreement include other payments based upon Genentech's achievement of milestones. Assuming all benchmarks are met, we will receive $39.5 million in upfront and milestone payments under this agreement. On January 27, 2006, Genentech notified us that the trastuzumab-DM1 Investigational New Drug (IND) application submitted by Genentech to the FDA had become effective. Under the terms of the May 2000 exclusive license agreement for the HER2 target, this event triggered a $2.0 million milestone payment to us. On May 4, 2006, we amended the May 2000 agreement. This amendment increases the potential milestone payments to us under this agreement by $6.5 million to $44 million and the potential royalties to us on any HER2-targeting TAP compound that may be developed by Genentech, including trastuzumab-DM1.

We entered into another agreement with Genentech in May 2000. This second collaboration provides Genentech with broad access to our maytansinoid technology for use with Genentech antibodies to other (non-HER2) targets. This agreement provides Genentech with a license to utilize our maytansinoid technology in its antibody product research efforts and an option to obtain product licenses to use our maytansinoid technology with antibodies to a limited number of antigen targets over the agreement's fiveyear term. Under this agreement, we received a non-refundable technology access fee of $3.0 million in May 2000. This agreement provides for payments for each antigen target licensed based on Genentech's achievement of milestones and royalties on net sales of resulting products, if and when such sales commence. Genentech renewed this agreement for one subsequent three-year period in April 2005 for an additional technology access fee of $2.0 million.

Under this agreement, in April 2005, July 2005 and December 2005, Genentech licensed exclusive rights to use our maytansinoid TAP technology with antibodies to three undisclosed targets. Under the terms defined in the 2000 "access" agreement, we received a $1.0 million license fee for each license, and is entitled to receive $38 million in milestone payments; we are also entitled to receive royalties on the sales of any resulting products. Genentech is responsible for the development, manufacturing, and marketing of any products resulting from these licenses.

In-Licenses

From time to time we may in-license certain rights to targets or technologies, in conjunction with our internal efforts to develop both TAP and naked antibody products and related technologies. In exchange, we may be obligated to pay upfront fees, potential milestone payments and royalties on any product sales.

Other Licenses

We also have licenses with third parties, including other companies and academic institutions, to gain access to techniques and materials for drug discovery and product development and the rights to use those techniques and materials to make our products. These licenses include rights to certain antibodies, software used in antibody development and apoptosis technology.

Other Agreements

BioInvent International AB

In June 2001, we entered into a monoclonal antibody supply agreement with BioInvent International AB. Under the terms of the agreement, BioInvent agreed to perform process qualification and manufacture one of our monoclonal antibodies pursuant to the cGMP requirements. Under the terms of the agreement, we pay a stated price per gram of antibody, adjustable based upon production volumes.

In December 2002, we entered into an additional supply agreement with BioInvent to produce a second monoclonal antibody. The monoclonal antibody that is the subject of the second agreement is a component of one of the products we licensed to sanofi-aventis. As further discussed in Item 7, Management's Discussion and Analysis of Financial Condition and Results of Operation, sanofi-aventis reimbursed us for $1.3 million, the full cost of the monoclonal antibody produced under this agreement. The $1.3 million was included in Other Income for the quarter and year ended June 30, 2004.

In June 2006, we entered into an additional supply agreement with BioInvent to produce additional quantities of a monoclonal antibody pursuant to the cGMP requirements. Under the terms of the agreement, we agreed to pay a stated price per manufactured batch of antibody, subject to adjustment as set forth in the agreement.

Diosynth RTP, Inc.

In August 2005, we entered into a bioprocessing services agreement with Diosynth RTP, Inc. Under the terms of the agreement, Diosynth agreed to perform technology transfer, process development and scale-up of the antibody component of one of our product candidates pursuant to the cGMP requirements. Under the terms of the agreement, ImmunoGen shall pay Diosynth a stated price for the technology transfer and process development.

Laureate Pharma, L.P.

In April 2004, we entered into a monoclonal antibody supply agreement with Laureate Pharma, L.P. Under the terms of the agreement, Laureate agreed to perform process qualification and manufacture one of our monoclonal antibodies pursuant to the cGMP requirements. Under the terms of the agreement, w e pay a stated price per manufactured batch of antibody, subject to adjustment as set forth in the agreement.

In December 2005, we entered into a second monoclonal antibody supply agreement with Laureate to produce additional quantities of the monoclonal antibody pursuant to cGMP requirements. Under the terms of the agreement, we pay a stated price per manufactured batch of antibody, subject to adjustment as set forth in the second agreement.

Societá Italiana Corticosteroidi S.r.l (SICOR)

Effective November 2004, we entered into a technology transfer and development agreement with SICOR. Under the terms of the agreement, SICOR agreed to perform a feasibility study and full process development work to produce DM1, a component of our TAP products. Under the terms of the agreement, we agreed to pay SICOR a stated price for work performed based on achievement of certain milestone events. On June 21, 2006, we amended the 2004 technology transfer and development agreement with SICOR. Under the terms of the amendment, SICOR also provides preparatory activities in order to scale-up the production of ansamitocin P3, a precursor to DMx compounds, in anticipation of large-scale production of ansamitocin P3 and DMx compounds to be used in TAP compounds for laterstage clinical trials and commercialization.

Patents, Trademarks and Trade Secrets

We seek patent protection for our proprietary technologies, product candidates, and related innovations in the United States, Europe, Japan and elsewhere. Patents that have been issued to us in the United States include the following: claiming a process for the preparation of certain maytansinoids; claiming methods of preparation of conjugates composed of maytansinoids and cell-binding agents; claiming composition and use of novel taxanes; claiming conjugates composed of taxanes and cell-binding agents; and a method of antibody humanization. In many cases, we have received comparable patents outside the United States.

We have also submitted additional patent applications in the United States, Europe, Japan, and elsewhere covering proprietary small drug derivatives, methods of attachment to antibodies, TAP compounds, antibody compounds and use of some of these product candidates and inventions for certain diseases. We expect that our work will also 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. We cannot provide assurance, however, 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.

In addition, 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. 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. Many of these companies and institutions also compete with us in recruiting highly qualified scientific personnel. 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:

Our competitive position depends on our ability to develop effective proprietary products, implement clinical development, production and marketing plans, including collaborations with other companies with greater marketing resources than ours, 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. In addition, monoclonal antibodies developed by certain of these companies have been approved for use as cancer therapeutics. In the future, additional monoclonal antibodies may compete with our product candidates.

Because of the prevalence of combination therapy in cancer and the variety of genes and targets implicated in cancer incidence and progression, we believe that products resulting from applications of new technologies may be complementary to our own.

Such new technologies include, but are not limited to:

Regulatory Matters

Our product candidates are regulated in the United States by the FDA in accordance with the United States Federal Food, Drug, and Cosmetic Act, as well as the Public Health Service Act. We expect that huC242-DM4, huN901-DM1 and other of our TAP compounds will be reviewed by the FDA's Center for Drug Evaluation and Research, or CDER. In addition, each drug manufacturer in the United States must be registered with the FDA.

The steps required before a new drug may be marketed in the United States include:

1. Performance of preclinical laboratory, animal, and formulation studies;
2. The submission to the FDA of an Investigational New Drug Application, which must become effective before clinical trials may commence;
3. The completion of adequate and well-controlled human clinical trials to establish the safety and efficacy of the drug;
4. The submission of a New Drug Application to and its acceptance by the FDA; and
5. FDA approval of the New Drug Application, including approval of product labeling and advertising.

Even if we, or our partners, obtain regulatory approvals for our product candidates, the Company, our products, and the facilities in which our products are manufactured are subject to continual review and periodic inspection. The FDA will require post-marketing reporting to monitor the safety of our products. Manufacturing establishments are subject to periodic inspections by the FDA and must comply with the FDA's current Good Manufacturing Practice, or cGMP. In complying with cGMP, manufacturers must expend funds, time and effort in the areas of production, quality control and recordkeeping to ensure full technical compliance. The FDA stringently applies regulatory standards for manufacturing.

The regulatory considerations that have potential impact on the future marketing of our products are summarized below.

Clinical Trials Process

Before a new drug may be sold in the United States and other countries, clinical trials of the product must be conducted and the results submitted to the appropriate regulatory agencies for approval.

In the United States, these clinical trial programs generally involve a three-phase process. Typically, Phase I trials are conducted in healthy volunteers to determine the early side-effect profile and the pattern of drug distribution and metabolism. In Phase II, trials are conducted in groups of patients afflicted with the target disease to determine preliminary efficacy and optimal dosages and to expand the safety profile. In Phase III, large-scale comparative trials are conducted in patients with the target disease to provide sufficient data for the proof of efficacy and safety required by federal regulatory agencies. In the case of drugs for cancer and other life-threatening diseases, Phase I human testing usually is performed in patients with advanced disease rather than in healthy volunteers.

We intend to conduct clinical trials not only in accordance with FDA regulations, but also within guidelines established by other applicable agencies and committees. Whether or not FDA approval has been obtained, approval of a product by the comparable regulatory authorities of foreign countries must be obtained prior to the commencement of marketing of the product in those countries. Regulatory approval in other countries is obtained through the various regulatory bodies governing pharmaceutical sales in those individual countries. We intend to rely on foreign licensees to obtain regulatory approvals to market our products in foreign countries.

Regulatory approval takes a number of years and involves the expenditure of substantial resources. Approval times also depend on a number of factors including, but not limited to, the severity of the disease in question, the availability of alternative treatments and the risks and benefits demonstrated in clinical trials.

Orphan Drug Designation

The Orphan Drug Act of 1983 generally provides incentives to biotechnology and pharmaceutical companies to undertake development and marketing of products to treat relatively rare diseases or diseases affecting fewer than 200,000 persons in the United States at the time of application for Orphan Drug designation.

We may pursue this designation with respect to products intended for qualifying patient populations. A drug that receives Orphan Drug designation and is the first product of its kind to receive FDA marketing approval for its product claim is entitled to a seven-year exclusive marketing period in the United States for that product claim.

New Drugs for Serious or Life-Threatening Illnesses

The FDA Modernization Act allows the designation of "Fast Track" status to expedite development of new drugs, including review and approvals, and is intended to speed the availability of new therapies to desperately ill patients. "Fast Track" procedures permit early consultation and commitment from the FDA regarding preclinical and clinical studies necessary to gain marketing approval. We may seek "Fast Track" status for some, or all, of our products.

"Fast Track" status also incorporates initiatives announced by the President of the United States and the FDA Commissioner in March 1996 intended to provide cancer patients with faster access to new cancer therapies. One of these initiatives states that the initial basis for approval of anticancer agents to treat refractory, hard-to-treat cancer may be objective evidence of response, rather than statistically improved disease-free and/or overall survival, as had been common practice. The sponsor of a product approved under this accelerated mechanism is required to follow up with further studies on clinical safety and effectiveness in larger groups of patients.

Research and Development Spending

During each of the three years ended June 30, 2006, 2005 and 2004, we spent approximately $40.9 million, $30.5 million and $21.7 million, respectively, on research and development activities. During the year ended June 30, 2006, approximately 58% of our full-time equivalent research and development personnel were dedicated to our sanofi-aventis collaboration compared to 60% during the years ended June 30, 2005 and 2004.

Employees

As of June 30, 2006, we had 192 full-time employees, of whom 152 were engaged in research and development activities. Eighty-four employees hold post-graduate degrees, of which 53 hold Ph.D. degrees and 5 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 agreemeSnts with all of our employees, members of the Board of Directors and consultants.

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.

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

Our TAP technology yields novel anticancer product candidates for the treatment of cancer. No TAP product candidate has obtained regulatory approval and all of them are in early stages of development. The most advanced TAP product candidates are only in the Phase I or Phase I/II stage of clinical trials. Our TAP product candidates or our collaborators' TAP product candidates may not prove to be safe, effective or commercially viable treatments for cancer and our TAP 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 one antibody-drug conjugate that has obtained FDA approval and is based on technology similar to our TAP technology. If our TAP technology fails to generate product candidates that are safe, effective and commercially viable treatments for cancer, or fails to obtain FDA approval, our business will be severely harmed.

Clinical trials for our 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. Our most advanced product candidates are only in the Phase I or Phase I/II stage of clinical trials. In our industry, the results from preclinical testing and early clinical trials often are not predictive of results obtained in later clinical trials. Some compounds that have shown promising results in preclinical 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 for our product candidates for various reasons, including:

The results of clinical trials may fail to demonstrate the safety or effectiveness of our product candidates or our collaborators' product candidates to the extent necessary to obtain regulatory approval or to make the commercialization of the product worthwhile. Any failure or substantial delay in successfully completing clinical trials and obtaining regulatory approval for our product candidates or our collaborators' product candidates could severely harm our business.

If our collaborative partners fail to p erform their obligations under our agreements, 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:

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, modify our existing arrangements on acceptable terms. We cannot control the amount and timing of resources our partners may devote to our products. Our partners may separately pursue competing products, 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 products under our agreements with them. Any of our partners may slow or discontinue the development of a product covered by a collaborative arrangement for reasons that can include:

Even if our partners continue the collaborative arrangements, they may nevertheless determine not to actively pursue the development or commercialization of any resulting products. Also, our partners may fail to perform their obligations under the collaborative agreements or may be slow in performing their obligations. Our 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, or fail to complete its obligations to us in a timely manner, our anticipated revenue from the agreement and from the development and commercialization of our 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, 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 TAP compounds, our business 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 a material 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 a material adverse effect on our financial condition. 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, its continued pursuit and emphasis on our product development program could be delayed, diminished or terminated.

If our collaborators' 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 ansamitocin P3, DM1, DM4, and linker, on behalf of our collaborators. In order to meet our commitments to our collaborators, 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 collaborators. If our collaborators do not require as much clinical material as we have contracted to produce, we may not be able to recover our investment in these components and we may suffer significant losses. For example, in February 2005, Boehringer Ingelheim discontinued development of bivatuzumab mertansine and in January 2006, Millennium discontinued development of MLN2704. In the periods subsequent to discontinuation of development, we can have significantly reduced demand for conjugated material. Specifically, the discontinuation of bivatuzumab mertansine has contributed to the decrease in clinical materials reimbursement in the year ended June 30, 2006.

In addition, we operate a conjugate manufacturing facility. A significant portion of the cost of operating this facility, including the cost of manufacturing personnel, is charged to the cost of producing clinical materials on behalf of our collaborators. If we produce fewer batches of clinical materials for our collaborators, less of the cost of operating the conjugate manufacturing facility will be charged to our collaborators and our financial condition could be adversely affected.

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, 2006, we had an accumulated deficit of $238.6 million. For the years ended June 30, 2006, 2005, and 2004, we generated losses of $17.8 million, $11.0 million and $5.9 million, respectively. We may never be profitable. We expect to incur substantial additional operating expe nses over the next several years as our research, development, preclinical testing, clinical studies and collaborator support activities increase. We intend to continue to invest significantly in our product candidates. Further, we expect to invest significant resources supporting our existing collaborators as they work to develop, test and commercialize TAP and other antibody compounds, and 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. None of our product candidates has generated any commercial revenue and our only revenues to date have been primarily from upfront and milestone payments, research and development support and clinical materials reimbursement from our collaborative partners. We do not expect to generate revenues from the commercial sale of our product candidates for several years, and we may never generate revenues from the commercial sale of 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.

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. None of our product candidates has been approved for sale in the United States or any foreign market. 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 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. In light of the limited regulatory history of monoclonal antibody-based therapeutics, regulatory approvals for our products may not be obtained without lengthy delays, if at all. Any FDA or other regulatory approvals of our product candidates, once obtained, may be withdrawn. The effect of government regulation may be to:

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

Even if we receive regulatory approval to market a particular product candidate, the approval could be conditioned on us conducting costly post-approval studies or could limit the indicated uses included in our labeling. Moreover, the product may later cause adverse effects that limit or prevent its widespread use, force us to withdraw it from the market or impede or delay our 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 may be slow to adapt, or we may never adapt, to changes in existing regulatory requirements or adoption of new regulatory requirements.

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

We rely on two third-party manufacturers to perform separate activities in the process of producing supplies of our cell-killing agents, DM1 and DM4. Significant problems at either of these manufacturers could negatively impact the development of our own compounds and those of our collaborators.

We rely on third-party suppliers to manufacture materials used to make TAP compounds. Our cell-killing agents DM1 and DM4 (collectively "DMx") are manufactured from a precursor, ansamitocin P3. As part of preparing to produce TAP compounds for later-stage clinical trials and commercialization, we are in the process of transitioning from our original supplier of ansamitocin P3 to a larger company with more commercial production experience. We believe we have ample inventory of ansamitocin P3 in place to meet the anticipated demands by us and our partners during the transition period. Should there be a serious problem with the transition to the new vendor, however, we would not be able to immediately obtain material from our original supplier and our ability to produce TAP compounds could be significantly impacted, which may impact our and our collaborators' product development activities including clinical testing. We also use a single supplier to convert ansamitocin P3 to DMx. Any problems experienced by this vendor could result in a delay or interruption in the supply of DMx to us until this vendor cures the problem or until we locate an alternative source of supply. Any delay or interruption in our supply of DMx could lead to a delay or interruption in our manufacturing operations and preclinical and clinical trials of our product candidates and our collaborators' product candidates, which could negatively affect our business. We are currently working with a potential additional supplier to develop the capabilities to supply these materials. We cannot assume that we will be able to reach agreement with this supplier on acceptable terms, or at all.

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 United States, 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 United States and other major healthcare markets have been proposed and adopted in recent years. For example, the United States 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 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. In addition, ongoing initiatives in the United States have 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 the manufacturing capabilities necessary to develop and commercialize our potential products.

Currently, we have only a conjugate manufacturing facility that we use to manufacture conjugated compounds for us and our collaborators for preclinical and initial clinical testing. 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 collaborators 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 clinical trials and commercialization of our potential products and are putting in place these suppliers. 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 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 may develop our manufacturing capacity in part by expanding our current facilities or building new facilities. Either of these activities would require substantial additional funds and we would need to hire and train significant numbers of employees to staff these facilities. We may not be able to develop manufacturing facilities that are sufficient to produce drug materials for clinical trials or commercial use. We and any third-party manufacturers that we may use must continually adhere to current Good Manufacturing Practice regulations enforced by the FDA through its facilities inspection program. If our facilities or the facilities of third-party manufacturers cannot pass a pre-approval plant inspection, the FDA will not grant approval to our product candidates. In complying with these regulations and foreign regulatory requirements, we and any of our third-party manufacturers will be obligated to expend time, money and effort on production, record-keeping and quality control to assure that our potential products meet applicable specifications and other requirements. If we or any third-party manufacturer with whom we may contract fail to maintain regulatory compliance, we or the third party may be subject to fines and/or manufacturing operations may be suspended.

We have only one conjugate manufacturing facility and any prolonged and significant disruption at that facility could impair our ability to manufacture products for clinical testing.

Currently, we are contractually obligated to manufacture Phase I and non-pivotal Phase II clinical products for companies licensing our TAP technology. We manufacture this material in a conjugate manufacturing facility. We only have one such manufacturing facility in which we can manufacture clinical products. Our current manufacturing facility contains highly specialized equipment and utilizes complicated 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 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.

Any inability to license from third parties their proprietary technologies or processes 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 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 anticipate relying on third parties to market and sell most of our primary product candidates. 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 collaborators do not gain market acceptance, our business will suffer.

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

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 drug 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 condi tions, and whether the physicians are already using competing products that satisfy their treatment objectives. Physicians, patients, third-party payo rs 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 pricing reductions, reduced gross margins and failure to achieve market acceptance for our potential products. Our competitors include pharmaceutical companies, biotechnology companies, and research institutions. Many of these organizations have substantially more experience and more capital, research and development, regulatory, manufacturing, sales, marketing, human and other resources than we do. As a result, they may:

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. In addition, our product candidates, if approved and commercialized, will compete against well-established, existing, therapeutic products that are currently reimbursed by government health administration authorities, private health insurers and health maintenance organizations. 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 technolo gy 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. Although we own several 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.

Also, patents and applications owned or licensed by us may become the subject of interference proceedings before the United States Patent and Trademark Office to determine priority of invention that could result in substantial cost to us. An adverse decision in an interference 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 challenge 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. 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 United States.

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. 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.

If we are forced to litigate or undertake other proceedings in order to enforce our intellectual property rights, we may be subject to substantial costs and liability or be prohibited from commercializing our potential products.

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. Any claims that might be brought against us alleging to 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 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.

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:

We may not have sufficient resources to satisfy any liability resulting from these claims. We currently have $5.0 million of product liability insurance for products which are in clinical testing. This 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 scientific personnel or to attract additional highly qualified personnel could delay the development of our product candidates and harm our business.

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 products.

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 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 future payments, if any, from our collaboration arrangements, including committed research funding that we expect to receive from sanofi-aventis pursuant to the terms of our collaboration agreement, will be sufficient to meet our current and projected operating and capital requirements for at least the next two to three years. However, we may need additional financing sooner due to a number of factors including:

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

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, as a result of market trends and as a result of our low stock price. The business developments that could impact our stock price include disclosures related to clinical findings with compounds that make use of our TAP technology, new partnerships, and clinical advancement or discontinuation of product candidates that make use of our TAP 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 und er our prior collaboration agreements may not be an indicator of revenue from any future collaborations. 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 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 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.

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.

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 report.

Forward-looking statements in this report include, but are not limited to:

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 report.

Item 1B. Unresolved Staff Comments

none

Item 2. Properties

We lease approximately 37,700 square feet of laboratory and office space in a building located at 128 Sidney Street, Cambridge, Massachusetts. The 128 Sidney Street lease expires on March 31, 2008; however, we have the option, subject to our landlord's approval, to extend the lease for an additional five-year term pursuant to an amendment dated August 29, 2001. We sublease approximately 15,000 square feet of laboratory and office space in a building located at 148 Sidney Street, Cambridge, Massachusetts. The 148 Sidney Street lease expires on October 31, 2010. We sublease approximately 7,000 square feet of space at 64 Sidney Street, Cambridge, Massachusetts for general and administrative purposes. The 64 Sidney Street sublease expires on March 31, 2008. We also lease approximately 35,450 square feet of space in Norwood, Massachusetts, which serves as the Company's conjugate manufacturing facility and office space. The Norwood lease expires on June 30, 2011, but we have the option to extend the lease for an additional five-year term pursuant to an amendment dated October 30, 2005. We believe that the manufacturing portion of the Norwood facility complies with all applicable current Good Manufacturing Practice regulations of the FDA.

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 4. Submission of Matters to a Vote of Security Holders

No matters were submitted to a vote of our security holders through solicitation of proxies or otherwise during the last quarter of the fiscal year ended June 30, 2006.

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