ImmunoGen, Inc. : Announces Presentation of New Clinical Data for SAR3419

ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company, today announced the presentation of new clinical data for the investigational compound, SAR3419, at the American Society of Clinical Oncology (ASCO) annual meeting taking place in Chicago, IL. SAR3419 uses ImmunoGen's Targeted Antibody Payload (TAP) technology and is a potential treatment for CD19+ non-Hodgkin's lymphoma (NHL) and other B-cell malignancies. The compound was created by ImmunoGen and licensed to Sanofi as part of a broader collaboration. The data reported today are from the Phase I evaluation that established the dosing schedule being used with SAR3419 in its Phase II evaluation.

"We believe the findings reported today support that SAR3419 has the potential to become an important new therapy for key B-cell malignancies," commented Daniel Junius, President and CEO. "These findings also add to the growing body of clinical data supporting that the utility of our TAP technology - and the depth of our product opportunities - extend well beyond any one compound to multiple types of cancers, antibodies, and product designs."

In its Phase I assessment, SAR3419 has been found to demonstrate activity across an array of NHL histological subtypes and in patients with rituximab (Rituxan^®)-refractory and -responsive disease.^1,2 Alternative dosing schedules were evaluated to establish the recommended Phase II schedule.

The findings reported today (abstract #8057) are from an extension of a weekly dosing Phase I trial. In this extension, SAR3419 was administered weekly for four weeks and then on an every two-week basis for another four doses. The study investigators note that this schedule "demonstrates an improved safety profile compared to prior tested schedules" while preserving antitumor activity:

• When dosed weekly (at 55 mg/m²), 33% (7/21) of patients had an objective response (a complete response/CR or partial response/PR).
• When the same dose level was administered with this modified schedule, 29% (6/21) of patients had an objective response and another 43% (9/21) had stable disease.

In October 2011, Sanofi advanced SAR3419 into Phase II clinical testing. In Phase II, the compound is being evaluated for the treatment of CD19+ diffuse large B-cell lymphoma (DLBCL) - alone and in combination with rituximab - and for B-cell acute lymphoblastic leukemia (B-ALL).

About SAR3419

SAR3419 is an investigational TAP compound that consists of a CD19-binding antibody developed by ImmunoGen with one of the Company's potent cell-killing agents, DM4, attached using one of its engineered linkers. The antibody enables the compound to bind specifically to cancer cells expressing its CD19 target and the DM4 serves to kill these cells.

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.

¹Younes, A. et al., ASH, Dec. 2009

²Coiffer B. et al., 11^th International conference on Malignant Lymphoma, June 2011

Rituxan^® is a registered trademark of Biogen Idec.

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 SAR3419, including risks related to clinical studies and their 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.

For Investors:
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info@immunogen.com
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