ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops anticancer therapeutics using its antibody expertise and Targeted Antibody Payload (TAP) technology, today announced the start of clinical testing with its IMGN529 product candidate. The Phase I trial initiated evaluates the safety, tolerability, pharmacokinetic profile and anticancer activity of escalating doses of IMGN529 in patients with non-Hodgkin's lymphoma (NHL) to establish the dose for future clinical trials.

Today NHL is frequently treated with the anticancer antibody, rituximab (Rituxan®), and/or with chemotherapy. The novel agent IMGN529, a TAP compound, contains a B-cell-targeting antibody that has demonstrated marked anticancer activity in preclinical testing.1 Attached to this antibody is a potent ImmunoGen cell-killing agent, DM1. The antibody serves: (1) to kill the cancer cells through multiple antibody-mediated mechanisms; and (2) to deliver the DM1 specifically to the cancer cells for additional, targeted anticancer potency.

"The Phase I trial now underway, together with our market research, is expected to provide the information needed to define a clear development path for IMGN529 in NHL," commented James O'Leary, MD, Vice President and Chief Medical Officer. "With its unique profile, we believe IMGN529 has the potential to be an important new therapy for the treatment of key B-cell malignancies."

About the Phase I Trial Initiated

This multi-center, first-in-human Phase I trial is expected to enroll approximately 55 patients with relapsed or relapsed/refractory, CD37-expressing NHL. Patients with follicular lymphoma, diffuse large B-cell lymphoma, mantle cell lymphoma, or marginal zone lymphoma - the more common types of NHL - are eligible for enrollment.

About IMGN529

ImmunoGen created IMGN529 for the treatment of B-cell malignancies that express its CD37 target. The prevalence of CD37 on malignant cells is similar to that of CD20, the target for rituximab: it is expressed widely on key NHL subtypes - including follicular lymphoma, diffuse large B-cell lymphoma, marginal zone lymphoma and mantle cell lymphoma - and also on chronic lymphocytic leukemia (CLL).1

IMGN529 contains a CD37-targeting ImmunoGen antibody that, in vitro, has been found to kill cancer cells through multiple mechanisms of action including pro-apoptotic activity, complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC).1,2 The attached DM1 kills cancer cells through a different mechanism - disruption of a key step that occurs during cell division.

About Non-Hodgkin's lymphoma

NHL comprises a diverse group of cancers that all derive from defects in cellular production of lymphocytes, a type of white blood cell. As the name suggests, NHL includes all lymphomas except Hodgkin's lymphoma. Approximately 85% of cases of NHL are B-cell lymphomas. It is estimated that, in the US, approximately 56,000 people are diagnosed with B-cell NHL each year and 16,000 die from the disease.3

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer therapeutics using the Company's expertise in tumor biology, monoclonal antibodies, potent cancer-cell killing agents and engineered linkers. The Company's TAP technology uses monoclonal antibodies to deliver one of ImmunoGen's proprietary cancer-cell killing agents specifically to tumor cells. There are now numerous TAP compounds in clinical development with a wealth of clinical data reported. ImmunoGen's collaborative partners include Amgen, Bayer HealthCare, Biotest, Lilly, Novartis, Roche, and Sanofi. The most advanced compound using ImmunoGen's TAP technology, trastuzumab emtansine (T-DM1), is in Phase III testing through the Company's collaboration with Genentech, a member of the Roche Group. More information about ImmunoGen can be found at www.immunogen.com.

1Mayo M. et al., AACR 2011, abstract #4581.
2Deckert J. et al., AACR 2011, abstract #4565.
3American Cancer Society, What is non-Hodgkin's Lymphoma.

Rituxan® is a registered trademark of Biogen Idec Inc.

This press release includes forward-looking statements. For these statements, ImmunoGen claims the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. It should be noted that there are risks and uncertainties related to the development of novel anticancer products, including IMGN529, including risks related to preclinical and clinical studies, their timings and results. A review of these risks can be found in ImmunoGen's Annual Report on Form 10-K for the fiscal year ended June 30, 2011 and other reports filed with the Securities and Exchange Commission.

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