ImmunoGen, Inc. Announces Overall Survival Data Reported for Trastuzumab Emtansine (T-DM1) Phase III EMILIA Trial

ImmunoGen, Inc. Announces Overall Survival Data Reported for Trastuzumab Emtansine (T-DM1) Phase III EMILIA Trial

<0> For Investors:ImmunoGen, Inc.Carol Hausner, 781-895-0600Executive Director, Investor Relations and Corporate CommunicationsorFor Media:The Yates NetworkBarbara Yates, 781-258-6153 </0>

(Nasdaq: IMGN), a biopharmaceutical company that develops anticancer products using its Targeted Antibody Payload (TAP) technology and antibody expertise, today announced the presentation of overall survival (OS) data from the trastuzumab emtansine Phase III trial, EMILIA. Trastuzumab emtansine is in global development by Roche under an agreement between ImmunoGen and Genentech, a member of the Roche Group, and utilizes ImmunoGen’s TAP technology with the trastuzumab antibody. Genentech and Roche have applied for marketing approval of trastuzumab emtansine in the US and Europe, respectively.

The EMILIA trial was designed to evaluate trastuzumab emtansine for the treatment of patients with metastatic HER2-positive breast cancer who have previously received trastuzumab (Herceptin®) and a taxane. Patients enrolled were randomized to treatment either with trastuzumab emtansine – used alone – or with lapatinib (Tykerb®) plus capecitabine (Xeloda®), standard-of-care in this setting. EMILIA progression-free survival (PFS) and tolerability findings were previously reported at the American Society of Clinical Oncology (ASCO) annual meeting in June 2012: patients treated with trastuzumab emtansine had a significant improvement in PFS (hazard ratio=0.65, p<0.0001) and experienced fewer Grade 3 or greater (severe) adverse events (40.8 percent vs. 57.0 percent) than those treated with standard-of-care. PFS and OS are co-primary endpoints of the EMILIA trial.

The OS data reported today showed that the risk of death was reduced by 32 percent for patients who received trastuzumab emtansine compared to those who received standard-of-care (hazard ratio=0.68, p=0.0006). Patients treated with trastuzumab emtansine survived a median of 5.8 months longer than those who received Tykerb plus Xeloda: median OS was 30.9 months for patients receiving trastuzumab emtansine versus 25.1 months for patients receiving standard-of-care.

“We’re thrilled that trastuzumab emtansine provided this significant overall survival benefit,” commented Daniel Junius, President and CEO. “We believe trastuzumab emtansine is an important new medicine and are hopeful it will advance into the hands of practicing oncologists as rapidly as possible.”

The data are being presented today at the ESMO 2012 Congress taking place in Vienna, Austria (abstract #LBA12; oral presentation at 2:10 pm CEST). The results of the EMILIA study are also being published today in the .

In HER2-positive breast cancer – Roche has Phase III trials underway evaluating trastuzumab emtansine both for newly diagnosed and for previously treated metastatic disease. It plans to initiate a trial program in early stage disease in 2013, with studies to evaluate the compound for adjuvant use, for neoadjuvant use, and as a treatment for patients with residual invasive disease following standard neoadjuvant therapy.

In HER2-positive gastric cancer – Roche is assessing trastuzumab emtansine for the treatment of advanced, relapsed HER2-positive gastric cancer.

A TAP compound consists of a monoclonal, or manufactured, antibody that binds specifically to a target found on tumor cells with one of the Company’s proprietary highly potent cancer-killing agents attached as a payload. The antibody serves to target the payload specifically to the cancer cells, and the payload serves to kill the cancer cells. Trastuzumab emtansine employs ImmunoGen’s non-cleavable SMCC linker and DM1 cancer-killing agent.

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-killing agents specifically to tumor cells. There are now ten TAP compounds in clinical development, of which three are wholly owned by the Company. Marketing applications for trastuzumab emtansine (T-DM1), the most advanced compound using ImmunoGen's TAP technology, have been submitted in the US and Europe. Roche is developing this compound globally under an agreement between ImmunoGen and Genentech, a member of the Roche Group. More information about ImmunoGen can be found at .

ASCO June 2012 (abstract #LBA1).

Tykerb® is a registered trademark of GlaxoSmithKline plc. Xeloda® is a registered trademark of Roche. Herceptin® is a registered trademark of Genentech, a member of the Roche Group.

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