Kristine Peterson - 12 Feb 2024 Form 4 Insider Report for ImmunoGen, Inc.

Footnote F1

This Form 4 reports securities disposed of pursuant to the terms of the Agreement and Plan of Merger (the "Merger Agreement"), dated November 30, 2023, by and among the Issuer, AbbVie Inc., a Delaware corporation ("AbbVie"), Athene Subsidiary LLC, a Delaware limited liability company and wholly owned subsidiary of AbbVie ("Intermediate Sub"), and Athene Merger Sub Inc., a Massachusetts corporation and wholly owned subsidiary of Intermediate Sub ("Purchaser"), pursuant to which Purchaser merged with and into the Issuer with the Issuer continuing as the surviving corporation (the "Merger").

Footnote F2

At the effective time of the Merger (the "Effective Time"), each restricted stock unit ("RSU") granted prior to the date of the Merger Agreement that was outstanding immediately prior to the Effective Time was canceled, and the Reporting Person was entitled to receive (without interest), in consideration of the cancellation of such RSU, an amount in cash (less any applicable withholding taxes) equal to (i) the number of shares of common stock, par value $.01 per share, of the Issuer ("Common Stock") subject to such RSU immediately prior to the Effective Time, multiplied by (ii) $31.26, without interest (the "Merger Consideration").

Footnote F3

Pursuant to the Merger Agreement, at the Effective Time, each deferred share unit ("DSU") granted prior to the date of the Merger Agreement that was outstanding immediately prior to the Effective Time was canceled, and the Reporting Person was entitled to receive (without interest), in consideration of the cancellation of such DSU, an amount in cash (less any applicable withholding taxes) equal to (i) the number of shares of Common Stock subject to such DSU immediately prior to the Effective Time, multiplied by (ii) the Merger Consideration.

Footnote F4

Pursuant to the Merger Agreement, at the Effective Time, each option to purchase shares of Common Stock ("Stock Option") granted prior to the date of the Merger Agreement that was outstanding immediately prior to the Effective Time was canceled, and the Reporting Person was entitled to receive (without interest), in consideration of the cancellation of such Stock Option, an amount in cash (less any applicable withholding taxes) equal to (i) the total number of shares of Common Stock subject to such Stock Option immediately prior to the Effective Time, multiplied by (ii) the excess, if any, of the Merger Consideration over the applicable exercise price per share of Common Stock under such Stock Option.