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): May 16, 2007

ImmunoGen, Inc.

(Exact name of registrant as specified in its charter)

128 Sidney Street, Cambridge, MA 02139

(Address of principal executive offices)   (Zip Code)

Registrant’s telephone number, including area code: (617) 995-2500

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.

(b)  ImmunoGen, Inc. (Nasdaq: IMGN) today announced the resignation of Howard Pien from the ImmunoGen’s Board of Directors. effective May 16, 2007. Mr. Pien recently accepted the position of President and Chief Executive Officer of Medarex, Inc. Since ImmunoGen and Medarex both develop antibody-based anticancer therapeutics, Mr. Pien’s new role with Medarex creates a conflict of interest with his role as a Director of ImmunoGen. ImmunoGen has initiated a search to replace Mr. Pien on its Board.

A copy of the press release  is attached hereto as Exhibit 99.1 and is incorporated by reference in this Item 5.02.

ITEM 9.01. FINANCIAL STATEMENTS AND EXHIBITS

(d): The following exhibit is being filed 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 INDEX

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Exhibit 99.1

Contacts:

For Immediate Release

ImmunoGen, Inc. Announces Resignation of Howard Pien

from its Board of Directors

– Mr. Pien’s New Position with Medarex Creates a Conflict of Interest –

CAMBRIDGE, MA, May 17, 2007 – ImmunoGen, Inc. (Nasdaq: IMGN) today announced the resignation of Howard Pien from the Company’s Board of Directors. Mr. Pien recently accepted the position of president and chief executive officer of Medarex, Inc. Since ImmunoGen and Medarex both develop antibody-based anticancer therapeutics, Mr. Pien’s new role with Medarex creates a conflict of interest with his role as a Director of ImmunoGen. The Company has initiated a search to replace Mr. Pien on its Board.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer biopharmaceuticals. The Company’s proprietary Tumor-Activated Prodrug (TAP) technology uses tumor-targeting antibodies to deliver a potent cell-killing agent specifically to cancer cells. Two TAP compounds wholly owned by ImmunoGen are in clinical testing – huN901-DM1 and huC242-DM4. Three anticancer compounds are in clinical testing through ImmunoGen’s collaborations with other companies – AVE9633 and AVE1642, in development by sanofi-aventis, and trastuzumab-DM1, in development by Genentech. Multiple compounds are in research/preclinical development.

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