Amendment: SEC Form SCHEDULE 13D/A filed by IGM Biosciences Inc.

Item 4 of the Prior Schedule 13D is hereby amended and supplemented in its entirety by adding the following paragraphs prior to the last paragraph of Item 4: The Tender Offer and the Merger On August 14, 2025, pursuant to the terms of the previously announced agreement and plan of merger, dated June 1, 2025 (the "Merger Agreement"), by an among the Issuer, Concentra Biosciences, LLC, a Delaware limited liability company ("Parent"), and Concentra Merger Sub V, Inc., a Delaware corporation and a wholly owned subsidiary of Parent ("Merger Sub"), Merger Sub completed its tender offer (the "Offer") to acquire all of the Issuer's issued and outstanding Common Stock and Non-Voting Common Stock (the "Issuer Shares") in exchange for (a) a price per share of $1.247 in cash (the "Offer Price"), subject to applicable tax withholding and without interest, plus (b) one contingent value right ("CVR") per share subject to the terms and conditions of the CVR Agreement described below (the "Purchase Price"). The Offer was subject to certain conditions, including among others that more than 50% of the Issuer's outstanding Common Stock be validly tendered in the Offer, inclusive of the shares of Common Stock owned by Parent and its affiliates. The Offer expired one minute following 11:59 p.m., Eastern Time, on August 13, 2025 (the "Offer Closing"). Redmile and the Redmile Funds tendered 100% of their Issuer Shares to Merger Sub by the Offer Closing in exchange for the aggregate Purchase Price. The Issuer Shares tendered by Redmile and the Redmile Funds included (a) 2,952,131 shares of Common Stock, and (b) 7,199,325 shares of Non-Voting Common Stock. On August 14, 2025, the Issuer completed the merger transaction with and into Merger Sub, with the Issuer surviving as a wholly owned subsidiary of Parent, pursuant to the terms of the Merger Agreement and applicable Delaware law (the "Merger"). At the effective time and date of the Merger (the "Merger Closing"), and without any action on the part of the Issuer stockholders, (a) each Issuer Share (other than those shares owned by (i) Parent, Merger Sub or any other Parent subsidiary after the Offer or (ii) any Issuer stockholders who are entitled to and who properly exercised their appraisal rights under Delaware law) automatically converted into the right to receive cash in the amount of the Offer Price; (b) each Pre-Funded Warrant was cancelled and the holder received the right to a cash amount based on the Offer Price, subject to applicable tax withholding and without interest, less the exercise price per share underlying the Pre-Funded Warrant, plus one CVR per underlying share subject to the terms and conditions of the CVR Agreement described below; (c) each in-the-money Option automatically vested and was cancelled and the holder received the right to a cash amount based on the Offer Price, subject to applicable tax withholding and without interest, less the exercise price per share underlying the Option, plus a CVR per underlying share subject to the terms and conditions of the CVR Agreement described below; and (d) each out-of-the-money Option was cancelled for no consideration. Immediately prior to the Merger Closing, Redmile beneficially owned 667,666 Pre-Funded Warrants, and all of the Options beneficially owned by Redmile were out-of-the-money. Immediately prior to the Offer Closing Time, Redmile beneficially owned 12,712 shares of Common Stock issued pursuant to fully vested RSUs granted to Michael Lee, a managing director of Redmile, in connection with his service as a member of the Issuer's Board of Directors. All of such shares were tendered in the Offer in exchange for the aggregate Purchase Price. Pursuant to the policies of Redmile, Mr. Lee held the Common Stock issued pursuant to the RSUs as a nominee on behalf, and for the sole benefit, of Redmile and its affiliates, and assigned all economic, pecuniary and voting rights in respect of the Common Stock issued pursuant to the RSUs to Redmile. Redmile and Mr. Green each disclaim beneficial ownership of such securities, except to the extent of its or his pecuniary interest in such securities, if any, and this Schedule 13D shall not be deemed an admission that the Reporting Persons are the beneficial owner of such securities any purpose. In connection with the Merger, Parent, Merger Sub and a rights agent entered into a contingent value rights agreement (the "CVR Agreement"), which provides that each CVR represents a contractual right to receive contingent cash payments equal to: (i) 100% of the amount by which Closing Net Cash (as finally determined pursuant to the Merger Agreement) exceeds $82.0 million, adjusted for any claims Parent reasonably determines to be valid five business days prior to the Merger Closing Date (as defined in the Merger Agreement) and that are not accounted for in such Closing Net Cash; and (ii) 80% of the Net Proceeds (as defined in the CVR Agreement), if any, from any sale, transfer, license or other disposition or grant of rights by Parent or any of its affiliates of all or any part of certain products and patents of the Issuer that occurs within the period beginning on the Merger Closing Date and ending on the first anniversary thereof. The foregoing descriptions of the Merger Agreement and the CVR Agreement do not purport to be complete and are qualified in their entirety by reference to the Merger Agreement and Form of CVR Agreement, copies of which are filed as Exhibit 2.1 and Exhibit 10.1, respectively, in the Issuer's Form 8-K filed on July 1, 2025 and are incorporated herein by reference. Resignation of Mike Lee from the Board of Directors Pursuant to the terms of the Merger Agreement, Michael Lee resigned from the Issuer's Board of Directors effective immediately prior to the Merger Closing.

Redmile: (1) Aggregate Number of Common Stock Beneficially Owned: 0 (2) Aggregate Percentage of Common Stock Beneficially Owned: 0.0% Jeremy C. Green: (1) Aggregate Number of Common Stock Beneficially Owned: 0 (2) Aggregate Percentage of Common Stock Beneficially Owned: 0.0%

Redmile: (1) Sole Voting Power: 0 (2) Shared Voting Power: 0 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 0 Jeremy C. Green: (1) Sole Voting Power: 0 (2) Shared Voting Power: 0 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 0

See the response to Item 4. Except as disclosed in Item 4, no reportable transactions were effected by any Reporting Persons during the past sixty days.

As of August 14, 2025, the Reporting Persons ceased to be the beneficial owners of more than five percent of the class of securities.

The information in Item 4 is incorporated herein by reference.