– Data Presented at the 13^th World Conference on Lung Cancer Demonstrate Favorable Tolerability and Promising Activity for SCLC and Related Tumors –

ImmunoGen, Inc. (Nasdaq: IMGN), a biopharmaceutical company that develops targeted anticancer therapeutics using its Targeted Antibody Payload (TAP) technology, today announced the presentation of encouraging initial efficacy, safety and tolerability clinical data with its IMGN901 product candidate in the treatment of small-cell lung cancer (SCLC). In two early-stage clinical trials that enrolled patients whose SCLC had recurred following treatment with standard chemotherapies, IMGN901 administration achieved notable tumor shrinkage and/or sustained stable disease. The compound also demonstrated encouraging activity against other CD56-expressing (CD56+) solid tumors. These clinical data are being presented at the 13^th World Conference on Lung Cancer taking place in San Francisco, CA, from July 31 to Aug. 4, 2009.

IMGN901 was created by ImmunoGen to kill tumors that express the CD56 protein targeted by the compound. It consists of a potent cancer-cell killing agent, DM1, attached to a CD56-targeting antibody, huN901, using an engineered linker. IMGN901 currently is in early clinical testing and is a potential treatment for SCLC, Merkel cell carcinomas, ovarian cancers, multiple myeloma, and other CD56+ cancers.

“We are encouraged by the initial efficacy and safety profile of IMGN901 in SCLC and Merkel cell carcinoma, especially as these cancers have proven highly challenging to treat,” stated Professor Penella J. Woll, MD, PhD, Weston Park Hospital, UK. “The data thus far indicate that IMGN901 offers potential for use in a number of indications, including several types of CD56-expressing solid tumors.”

The findings being presented at the 13^th World Conference on Lung Cancer by Professor Woll come from the two IMGN901 trials that included SCLC patients. Study 001 (enrollment has closed) was open to patients with any type of CD56+ solid tumor, including SCLC, during its dose-escalation Phase I leg. In its Phase II leg, enrollment was limited to patients with SCLC or other CD56+ small-cell carcinoma. In this trial, IMGN901 was administered weekly for four weeks every six weeks. Study 002 (enrollment is ongoing) is a dose-escalation trial evaluating IMGN901 in patients with CD56+ solid tumors, including SCLC, when administered daily for three consecutive days every 21 days. In both trials, the SCLC must have recurred following previous treatment with standard therapies for a patient to qualify for enrollment.

SCLC Clinical Data Reported

To date, 68 SCLC patients have been treated with IMGN901. All of these patients had received prior chemotherapy, and most had received at least two previous regimens. Among the findings were:

• The estimated clinical benefit rate was 25%, consisting of patients with an objective response and/or sustained stable disease (non-progression for at least 77 days).
• An objective response was reported in a patient whose SCLC had recurred within four months of treatment with cisplatin, etoposide, and topotecan plus radiation therapy. This patient had a partial response (PR) after his first IMGN901 treatment cycle and reached a 91% reduction in tumor size by the end of his third cycle. His disease progressed after his fourth cycle – 24 weeks after he first received IMGN901.
• Another SCLC patient had an objective response (an unconfirmed PR) and no evidence of disease progression for more than 8 weeks.