Daniel Junius, President and Chief Executive Officer, commented, “Amgen has an established track record of success in oncology and an expanding presence in antibody-based therapeutics. Amgen’s interest in antibody-drug conjugates is good for the field, and we’re pleased they’ve chosen to move forward with ImmunoGen’s technology.”

This license was taken under an agreement established in 2000 between ImmunoGen and Abgenix, Inc., which later was acquired by Amgen. Under the terms of the license, ImmunoGen receives a $1 million license payment upfront. The Company also is entitled to receive milestone payments potentially totaling $34 million plus royalties on the sales of any resulting products. Amgen is responsible for the development, manufacturing, and marketing of any products resulting from this license.

The agreement established in September 2000 grants Amgen certain rights to test ImmunoGen’s maytansinoid TAP technology with antibodies to specific targets and to license – on agreed-upon terms – the right to use the technology with antibodies to these targets to develop products.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer therapeutics using its expertise in cancer biology, monoclonal antibodies and the creation and attachment of potent cell-killing agents. The Company’s TAP technology uses antibodies to deliver one of ImmunoGen’s proprietary cell-killing agents specifically to cancer targets. In addition to the Company’s product pipeline, compounds utilizing the TAP technology are in clinical testing through ImmunoGen’s collaborations with Genentech (a wholly-owned member of the Roche Group), sanofi-aventis, Biogen Idec and Biotest. The most advanced compound, trastuzumab-DM1 (T-DM1), is in Phase III testing being conducted by Genentech and Roche. Other ImmunoGen collaborative partners include Bayer HealthCare and Amgen.

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 our collaborators, including Amgen, using our technology to develop products, including risks related to uncertainties around product advancement, study findings 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, 2009 and other reports filed with the Securities and Exchange Commission.

Contact:

ImmunoGen, Inc. Carol Hausner, 781-895-0600 Executive Director, Investor Relations and Corporate Communications info@immunogen.com