ImmunoGen announces underwriter's exercise of over-allotment option

ImmunoGen, Inc. (Nasdaq: IMGN), a biopharmaceutical company that develops targeted anticancer therapeutics, announced today that the underwriters of its previously announced public offering of common stock have exercised in full their option to purchase 1,350,000 shares of common stock at a public offering price of $8.00 per share. The exercise of the over-allotment option brings the total shares of common stock to be sold by ImmunoGen in the offering to 10,350,000 shares. Net proceeds, after underwriting discounts and commissions and estimated expenses, will be approximately $77.6 million. The offering is expected to close on or about May 12, 2010, subject to satisfaction of customary closing conditions.

J.P. Morgan Securities Inc. is acting as the sole book-runner for the offering and Oppenheimer & Co. Inc., RBC Capital Markets Corporation, Cantor Fitzgerald & Co. and Morgan Joseph & Co. Inc. are acting as co-managers.