ImmunoGen, Inc. Announces IMGN901 Clinical Data Presented at ASH

Benefit seen in both lenalidomide-naïve and lenalidomide-refractory multiple myeloma

ImmunoGen, Inc. Announces IMGN901 Clinical Data Presented at ASH

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

(NASDAQ: IMGN), a biotechnology company that develops anticancer therapeutics using its Targeted Antibody Payload (TAP) technology and antibody expertise, today announced the presentation of new clinical data with the Company’s targeted anticancer compound, IMGN901. The data were from a Phase I clinical study assessing IMGN901 used in combination with lenalidomide (Revlimid) and dexamethasone to treat patients with CD56-expressing relapsed or relapsed/refractory multiple myeloma. The data were reported in an oral presentation (abstract #728) at the 54 American Society of Hematology (ASH) Annual Meeting and Exposition in Atlanta, Georgia.

“The level and duration of the responses to the study regimen confirm the activity seen with IMGN901 in earlier trials – where it was evaluated as single-agent therapy – and support the further development of IMGN901 as a treatment for CD56-expressing cancers,” commented James O’Leary, MD, Vice President and Chief Medical Officer.

The trial was designed to assess IMGN901, given weekly for three weeks in a 4-week cycle, used in combination with lenalidomide and dexamethasone. As reported previously, a dose of 75 mg/m/week was established for IMGN901 in the dose-finding phase of the trial for evaluation in its expansion phase. Patients received lenalidomide and dexamethasone at standard doses (25 mg daily for 21 days in a 4-week cycle and 40 mg weekly for four weeks, respectively).

A total of 44 patients with relapsed or relapsed/refractory multiple myeloma were enrolled in the trial. Most of the patients had previously received bortezomib (Velcade®) (91%) and/or lenalidomide (59%), and many had received prior thalidomide (46%). Many patients also had received prior alkylating agents (64%) and/or anthracyclines (41%). About half of the patients had prior stem cell transplant.

The response findings reported for the 39 efficacy-evaluable patients included:

Of particular note, median time-to-progression was 7.7 months with the study regimen (IMGN901 at 75 mg/m).

The safety profile was consistent with the previously observed profiles of the drugs. The most common adverse events associated with the study regimen (occurring in >25% patients) consisted of Grade 1/2 peripheral neuropathy, fatigue, neutropenia, thrombocytopenia, nausea and diarrhea. Of note, the majority of patients entering the trial had Grade 1 peripheral neuropathy from prior therapy.

IMGN901, also known as lorvotuzumab mertansine, is wholly owned by ImmunoGen and consists of the Company's DM1 cancer-cell killing agent attached to its lorvotuzumab CD56-binding antibody using one of the Company’s engineered linkers.

Encouraging findings have been reported with IMGN901 in initial evaluations for the treatment of multiple myeloma, small-cell lung cancer (SCLC), and Merkel cell carcinoma (MCC). IMGN901 is in Phase II testing, in the NORTH trial, for front-line treatment of SCLC. It has been granted orphan drug designation for multiple myeloma, SCLC, and MCC in the US and Europe.

ImmunoGen, Inc. develops targeted anticancer therapeutics using its TAP technology together with the Company’s expertise in monoclonal antibodies and tumor biology. A TAP compound uses a tumor-targeting monoclonal antibody to deliver one of ImmunoGen's purpose-developed cancer-killing agents specifically to tumor cells. Ten TAP compounds are now in clinical testing, 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, are under review 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 .

Revlimid is a registered trademark of Celgene Corporation.Velcade® is a registered trademark of Millennium Pharmaceuticals, Inc.

Durie et al. . 2006

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