First clinical data for ImmunoGen's IMGN388 anticancer compound presented at ASCO Annual Meeting

ImmunoGen, Inc. (Nasdaq: IMGN), a biopharmaceutical company that develops targeted anticancer therapeutics, today announced the presentation of the first clinical data for the Company's IMGN388 anticancer compound at the 2010 Annual Meeting of the American Society of Clinical Oncology (ASCO) being held in Chicago, IL. In this dose-escalation trial, IMGN388 has demonstrated favorable tolerability at the dose levels evaluated to date, and evidence of activity is being reported now that higher doses are starting to be evaluated. Dose escalation is continuing.

“We're encouraged by the clinical findings with IMGN388”

"We're encouraged by the clinical findings with IMGN388," commented James O'Leary, MD, Vice President and Chief Medical Officer. "It's been well tolerated at the doses evaluated to date. This has enabled rapid advancement to dose levels where we'd expect to begin seeing evidence of activity and that has started to occur. We're using this trial to inform the next steps in IMGN388's development, which we expect to include its assessment as part of a combination regimen and potentially in specific types of cancer."

IMGN388

IMGN388 is in development by ImmunoGen for the treatment of solid tumors. It utilizes the Company's Targeted Antibody Payload (TAP) technology and consists of ImmunoGen's DM4 cancer-cell killing agent attached to an αv integrin-targeting antibody using the Company's method of attachment. The antibody component serves to target IMGN388 to αv integrin-expressing cells and the DM4 serves to kill these cells. The compound's integrin target is expressed on a wide variety of solid tumors and also on endothelial cells in the process of forming new blood vessels (angiogenesis), a process that needs to occur in order for solid tumors to grow.

Clinical Data Reported

The data reported today (Abstract #3058) are from the first clinical trial to be conducted with IMGN388. In the dose-escalation phase of this trial, patients with any type of solid tumor are eligible for enrollment. Once the maximum tolerated dose has been established, enrollment will be limited to patients with solid tumors confirmed to express its αv integrin target. To date, doses ranging from 5 to 130 mg/m² have been evaluated, IMGN388 has been found to be well tolerated, and dose escalation is continuing.

The evidence of activity reported is increasing with escalating dose levels:

• Among patients receiving 5, 10, 20 or 30 mg/m² - no evidence of activity;
• Among patients receiving 45 or 60 mg/m² - one patient at each dose level had stable disease lasting for up to 6 treatment cycles (18 weeks); and
• Among patients receiving 80 or 105 mg/m² - four of these six patients had stable disease. This response was ongoing in two patients at the time of the presentation and had been sustained for at least 7 treatment cycles (21 weeks) in one of these patients.

All of the patients treated with 130 mg/m² were still on study, but had not been followed for sufficient time for inclusion in the efficacy analysis.

The responses to IMGN388 occurred in an array of tumor types - non-small cell lung cancer (two patients) and in prostate, breast, neuroendocrine and uterine cancer. All of these patients had relapsed disease.