ImmunoGen, Inc. (Nasdaq: IMGN) today announced the presentation of interim data from the ongoing Phase I trial of Sanofi’s SAR566658 at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics meeting (abstract #A73) being held in Boston. SAR566658 is an ADC targeted to CA6, which is found on many cases of ovarian, breast, and other epithelial cancers. The data reported support that SAR566658 is generally well tolerated and can induce objective responses and sustained stable disease in heavily pretreated patients with CA6-positive cancers. SAR566658 was created by ImmunoGen and licensed preclinically to Sanofi as part of a broader collaboration between the companies. It comprises the Company’s huDS6 CA6-targeting antibody with one of ImmunoGen’s proprietary cell-killing agents (DM4) attached using one of its engineered linkers (SPDB). The interim findings reported today are from the dose-finding part of the first SAR566658 clinical trial. A total of 34 patients received SAR566658 at doses ranging from 10-240 mg/m 2 (6.5 mg/kg), administered every three weeks. Overall, SAR566658 was well tolerated, with limited adverse events typically associated with cytotoxic chemotherapy (hematologic toxicity, peripheral neuropathy). Reversible ocular corneal changes were seen at the higher doses. The recommended dose for further evaluation was determined to be 190 mg/m 2, and SAR566658 is now being assessed at that dose in the extension phase of the trial. Among the 20 patients who received SAR566658 at doses of 120 mg/m 2 (3.2 mg/kg) or more, there were two partial responses (PR), two unconfirmed PRs, and nine with stable disease. “These early clinical data indicate SAR566658 is generally well tolerated and can have anticancer activity against heavily pretreated CA6-positive tumors,” commented John Lambert, PhD, EVP and Chief Scientific Officer. “They also provide further support that our maytansinoid ADC technology can achieve active, well-tolerated anticancer compounds.” About ImmunoGen, Inc. ImmunoGen, Inc. develops targeted anticancer therapeutics. The Company’s ADC technology uses a tumor-targeting engineered antibody to deliver one of ImmunoGen's highly potent cancer-cell killing agents specifically to tumor cells. The most advanced compound with ImmunoGen’s ADC technology is Roche’s Kadcyla ®, which is marketed in the US by Genentech and is also gaining approvals internationally. ImmunoGen has four wholly owned clinical-stage product candidates, with additional compounds in the clinic through its partnerships with Amgen, Bayer HealthCare, Biotest and Sanofi. More information about ImmunoGen can be found at www.immunogen.com. Kadcyla ® is a registered trademark of Genentech, Inc., a member of the Roche Group. This press release includes forward-looking statements. For these statements, ImmunoGen claims the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. It should be noted that there are risks and uncertainties related to the development of novel anticancer products, including SAR566658. A review of these risks can be found in ImmunoGen's Annual Report on Form 10-K for the fiscal year ended June 30, 2013 and other reports filed with the Securities and Exchange Commission.