UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): July 29, 2008

ImmunoGen, Inc.

(Exact name of registrant as specified in its charter)

830 Winter Street, Waltham, MA 02451

(Address of principal executive offices)   (Zip Code)

Registrant’s telephone number, including area code: (781) 895-0600

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

o    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

ITEM 5.02 – DEPARTURE OF DIRECTORS OR CERTAIN OFFICERS; ELECTION OF DIRECTORS; APPOINTMENT OF CERTAIN OFFICERS; COMPENSATORY ARRANGEMENTS OF CERTAIN OFFICERS

(a)  Not applicable.

(b)  On July 29, 2008, Mitchel Sayare, Ph.D., resigned from his position as President of ImmunoGen, Inc. (the “Company”) in connection with the appointments described below. Dr. Sayare remains ImmunoGen’s Chairman of the Board and Chief Executive Officer.

(c)  On July 29, 2008, the Company’s Board of Directors appointed Daniel M. Junius as President and Chief Operating Officer and Acting Chief Financial Officer. At the same time, the Board appointed John M. Lambert, Ph.D., as Executive Vice President, Research and Development and Chief Scientific Officer.

Additional biographical information concerning Mr. Junius and Dr. Lambert is contained in the Company’s press release dated July 31, 2008, which is incorporated herein by reference.

(d)  Not applicable.

(e)  On July 30, 2008, the Compensation Committee of the Company’s Board of Directors voted to increase Mr. Junius’s annual base salary to $382,016, and to increase Dr. Lambert’s annual base salary to $328,390, effective in each case as of July 29, 2008. The Compensation Committee also adjusted the executives’ target cash bonuses under the Company’s annual executive bonus program to 40% of annual base salary, in the case of Mr. Junius, and 35% of annual base salary, in the case of Dr. Lambert.

ITEM 9.01. FINANCIAL STATEMENTS AND EXHIBITS

(d): The following exhibit is being furnished herewith:

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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Exhibit 99.1

Contact:

For Immediate Release

ImmunoGen, Inc. Announces Senior Management Promotions

– Daniel M. Junius named President and Chief Operating Officer –

– John M. Lambert, Ph.D., named Executive Vice President –

WALTHAM, MA, July 31, 2008 – ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops targeted anticancer products, today announced two senior management promotions. Daniel M. Junius has been named President and Chief Operating Officer. John M. Lambert, Ph.D., has been named Executive Vice President, Research and Development, and will continue as ImmunoGen’s Chief Scientific Officer.

“In the three years he’s been with us, Dan has made very important contributions to positioning ImmunoGen for success as the Company evolves from an organization focused principally on research to one with a significant clinical pipeline. We look forward to Dan’s leadership in his new capacities as our programs and those of our collaborators continue to advance,” commented Mitchel Sayare, Chairman and Chief Executive Officer. “John, in turn, has a phenomenal wealth of scientific expertise in our field that both we and our collaborators find invaluable. His expertise is highly complementary to Dan’s. John’s promotion to Executive Vice President reflects the tremendous value John has added to our organization as our head of research.”

Daniel M. Junius, President and Chief Operating Officer

Prior to his promotion to this newly created position, Mr. Junius, age 55, was Executive Vice President and Chief Financial Officer (CFO) of ImmunoGen with responsibility for the Company’s financial, planning, manufacturing, and administrative functions. With this promotion, Mr. Junius gains responsibility for the remaining corporate functions, including research, clinical development, regulatory, business development and alliance management. ImmunoGen has initiated a search for a chief financial officer and, until the position is filled, Mr. Junius also will continue to function in that capacity.

Mr. Junius joined ImmunoGen in May 2005 as Senior Vice President, Finance and CFO with over twenty years of business experience. He was promoted to Executive Vice President, Finance and CFO in July 2006. Mr. Junius had been Executive Vice President

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and CFO of New England Business Service, Inc. (NEBS) from 1998 until its acquisition by Deluxe Corporation in 2004. Prior to NEBS, he was Vice President and CFO of Nashua Corporation. Mr. Junius joined Nashua Corporation in 1984 and held financial management positions of increasing responsibility before becoming its CFO in 1996. He has a Masters in Management from Northwestern University’s Kellogg School of Management.

John M. Lambert, Ph.D., Executive Vice President, Research and Development and Chief Scientific Officer

Prior to this promotion, Dr. Lambert, age 56, was Senior Vice President, Research and Development and Chief Scientific Officer of ImmunoGen. John M. Lambert joined the Company in 1987 as Senior Director of Research and was promoted to Vice President, Research and Development in 1994, to Senior Vice President, Pharmaceutical Development in 2000 and then to Senior Vice President, Research and Development and Chief Scientific Officer in early 2008. Prior to his tenure with ImmunoGen, Dr. Lambert was Assistant Professor of Pathology at the Dana-Farber Cancer Institute in Boston, MA. Dr. Lambert received his doctorate in Biochemistry from Cambridge University in England.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer therapeutics using its expertise in cancer biology, monoclonal antibodies, and the creation and attachment of potent cell-killing agents. The Company’s Tumor-Activated Prodrug (TAP) technology uses antibodies to deliver one of ImmunoGen’s proprietary cell-killing agents specifically to cancer targets. In addition to the Company’s proprietary clinical pipeline, ImmunoGen collaborators Genentech, sanofi-aventis and Biogen Idec also are testing TAP compounds in the clinic, and a naked antibody is in clinical trials through the Company’s collaboration with sanofi-aventis.

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