First Clinical Data Presented with IMGN853, ImmunoGen, Inc.’s Potential New Therapy for Ovarian and Other Cancers

First Clinical Data Presented with IMGN853, ImmunoGen, Inc.’s Potential New Therapy for Ovarian and Other Cancers

<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>

ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops anticancer therapeutics using its Targeted Antibody Payload (TAP) ADC technology, today announced the presentation of the first clinical data with the Company’s IMGN853 product candidate. The data are from the ongoing dose-finding portion of a Phase I clinical assessment of the compound, which is a potential treatment for many ovarian, endometrial, and non-small cell lung cancers, as well as other FRα-overexpressing cancers. The data are being presented (abstract #2573) at the American Society of Clinical Oncology (ASCO) annual meeting taking place in Chicago, IL.

The dose-finding portion of this Phase I clinical trial is designed to establish the maximum tolerated dose of IMGN853 and to define its dose-limiting toxicity (DLT). Patients with any type of cancer known to overexpress IMGN853’s FRα target are eligible for enrollment in this phase of the trial. Once the maximum tolerated dose is established, IMGN853 will be evaluated in patients with specific types of FRα-overexpressing cancers, with prescreening to ensure tumor levels of FRα-overexpression meet defined criteria.

At the time of data cutoff for presentation, 18 patients had received IMGN853 at doses ranging from 0.15 to 7.0 mg/kg. DLT, seen at 7.0 mg/kg, was reversible blurred vision with epithelial corneal changes. The patients assigned to this dose were reduced to 5.0 mg/kg, the second highest dose evaluated. Additional new patients are being treated with 5.0 mg/kg to further assess that dose.

While this assessment is designed to evaluate the safety of IMGN853 and establish its maximum tolerated dose, evidence of clinical activity is also identified. Activity started to be seen when dose levels reached 3.3 mg/kg and included:

All three of these patients had cancer that scored strongly positive for IMGN853’s FRα target, as determined by well-established immunohistochemistry (IHC) assessment.

“We are highly encouraged by these initial clinical findings with IMGN853,” commented Dr. Charles Morris, Executive Vice President and Chief Development Officer. “Preliminary evidence of activity has been seen in the dose-finding portion of this trial. We look forward to completing this part of the trial and beginning evaluation of IMGN853 in disease-specific patient populations.”

ImmunoGen expects to begin the disease-specific, dose-expansion phase of this trial later this year. In that phase, IMGN853 will be evaluated in patients who have been prescreened for specific levels of FRα-overexpression and have either: (1) platinum-resistant ovarian cancer treated with three or fewer prior regimens; (2) relapsed/refractory ovarian cancer treated with less strictly defined prior therapies; or (3) adenocarcinoma non-small cell lung cancer. Addition of a cohort to assess IMGN853 for endometrial cancer is now also planned.

IMGN853 is a FRα-targeting ADC wholly owned by ImmunoGen. It comprises three components developed by Company scientists: a humanized FRα-binding antibody, which serves to target the compound to FRα-expressing cancer cells; DM4, a potent cell-killing agent; and an engineered linker, which serves to keep the DM4 attached to the antibody en route to the cancer cells and also – once inside a cancer cell – helps counter the multi-drug resistance that can make previously treated cancers harder to kill.

IMGN853 is in Phase I testing for the treatment of FRα-overexpressing cancers, which include many ovarian, endometrial and adenocarcinoma non-small cell lung cancers.

Each year, there are approximately 22,000 new cases of ovarian cancer diagnosed in the US and more than 14,000 women die from the disease. Epithelial ovarian cancer accounts for approximately 85% to 90% of all cases of ovarian cancer.

An estimated 48,500 cases of endometrial cancers will be diagnosed in the US in 2013 and approximately 8,000 women will die from the disease.

Each year, approximately 228,000 patients in the US are diagnosed with lung cancer and approximately 160,000 die from the disease. About 40% of lung cancers are the adenocarcinoma subtype of non-small cell lung cancer.

ImmunoGen, Inc. develops targeted anticancer therapeutics. The Company’s TAP technology uses a tumor-targeting monoclonal antibody to deliver one of ImmunoGen's highly potent cancer cell-killing agents specifically to tumor cells. Ten TAP compounds are now in the clinic, of which three are wholly owned by the Company. The most advanced compound using ImmunoGen's TAP technology, Kadcyla™, has been approved for marketing in the US and Switzerland, and is undergoing regulatory review in the European Union and Japan. Kadcyla is being commercialized in the US by Genentech, a member of the Roche Group. More information about ImmunoGen can be found at .

Kadcyla™ is a trademark of Genentech.

Target expression rated 3 on scale of 0-3. IHC method described in Carrigan et al., AACR 2011, abstract #3617. American Cancer Society (2013), . American Cancer Society (2013), . American Cancer Society (2013), . American Cancer Society (2013), .

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