Amendment: SEC Form SCHEDULE 13D/A filed by Merus N.V.

Item 3 of the Schedule 13D is amended and restated in its entirety as follows: "The Reporting Persons financed the purchase of Common Shares that are the subject of this Schedule 13D and Amendment No. 1 thereto through a combination of (i) proceeds from the issuance of $1.5 billion of 6.250% senior secured notes due 2032, pursuant to the indenture governing the notes, dated December 3, 2025 (the "Secured Notes Indenture"), a copy of which is attached as Exhibit F to this Schedule 13D, (ii) proceeds from the issuance of $1.0 billion of 7.250% senior unsecured notes due 2033, pursuant to the indenture governing the notes, dated December 3, 2025 (the "Unsecured Notes Indenture"), a copy of which is attached as Exhibit G to this Schedule 13D, (iii) proceeds from a $1.0 billion term loan A facility and a $2.0 billion term loan B facility borrowed under the Credit Agreement, dated December 12, 2025, among Parent and Genmab Finance LLC, as co-borrowers, the lenders from time to time party thereto and Morgan Stanley Senior Funding, Inc., as Administrative Agent and Collateral Agent (the "Credit Agreement"), a copy of which is attached as Exhibit H to this Schedule 13D, and (iv) existing cash on hand. The foregoing summary is qualified in its entirety by the full text of the Offer to Purchase, the Secured Notes Indenture, the Unsecured Notes Indenture and the Credit Agreement, which are filed as exhibits to this Schedule 13D and incorporated herein by reference."

Item 4 of the Schedule 13D is amended and restated in its entirety as follows: "The purpose of the transactions described in this Schedule 13D is for the Reporting Persons to acquire control of all of the issued and outstanding Common Shares of the Issuer while allowing all of the Issuer's shareholders an opportunity to receive the purchase price of $97.00 per Common Share by tendering their Common Shares pursuant to the Offer. At 5:00 p.m. New York City time on December 29, 2025, the Subsequent Offering Period expired. The Common Shares ceased to trade on Nasdaq prior to the opening of trading on December 30, 2025, and Nasdaq has filed with the SEC a Notification of Removal from Listing and/or Registration under Section 12(b) of the Exchange Act on Form 25 to delist the Common Shares from Nasdaq and deregister the Common Shares under Section 12(b) of the Exchange Act. In addition, after the Form 25 becomes effective, Purchaser intends to cause the Issuer to file with the SEC a Certification and Notice of Termination of Registration on Form 15 and take steps to cause the suspension of all of the Issuer's reporting obligations to the SEC with respect to the Common Shares. The information set forth in the section of the Offer to Purchase entitled "Summary Term Sheet" and "Purpose of the Offer; Back-End Transactions; Plans for Merus" is incorporated herein by reference. The foregoing summary is qualified in its entirety by the full text of the Offer to Purchase, which are filed as exhibits to this Schedule 13D and incorporated herein by reference. The information set forth under Item 5 of this Schedule 13D is incorporated herein by reference."

Item 5(a) and Item 5(b) of the Schedule 13D are hereby amended and restated in their entirety as follows: "The information contained on the cover pages to Amendment No. 1 is incorporated herein by reference. Parent, by virtue of its relationship to Purchaser (as disclosed in Item 2), may be deemed to indirectly beneficially own (as such term is defined in Rule 13d-3 under the Act) the Common Shares which Purchaser directly beneficially owns. On December 12, 2025, following the expiration of the initial offering period of the Offer at 5:00 p.m., New York City time on December 11, 2025, Purchaser accepted for payment, and thus acquired, 71,463,077 Common Shares tendered pursuant to the Offer (representing approximately 94.8% of the Issuer's outstanding Common Shares based upon the 75,865,294 Common Shares outstanding as of December 12, 2025, according to Equiniti Trust Company, LLC, in its capacity as depositary for the Offer (the "Depositary")), in exchange for the Offer Consideration, less any applicable withholding taxes and without interest. In addition, on December 12, 2025, Purchaser commenced a subsequent offering period (the "Subsequent Offering Period"), which expired at 5:00 p.m., New York City time on December 29, 2025. During the Subsequent Offering Period, Purchaser accepted for payment, and thus acquired, 2,421,216 additional Common Shares (representing approximately 3.19% of the Issuer's outstanding Common Shares based upon the 75,867,199 Common Shares outstanding as of December 29, 2025, according to the Depositary), in exchange for the Offer Consideration, less any applicable withholding taxes and without interest. In accordance with the Transaction Agreement, Parent and Purchaser consummated the Back-End Merger effective as of 6:00 p.m. New York City time on December 29, 2025 (12:00 a.m. Central European Time on December 30, 2025) and the Back-End Cancellation effective as of 6:30 p.m. New York City time on December 29, 2025 (12:30 a.m. Central European Time on December 30, 2025). Pursuant to the Back-End Merger and the Back-End Cancellation, each Common Share held by shareholders of the Issuer (other than Purchaser) as of immediately prior to the Back-End Merger (each, a "Minority Shareholder") was cancelled and converted into the right to receive an amount in cash equal to the Offer Consideration multiplied by the number of Common Shares held by such Minority Shareholder immediately prior to the Back-End Merger (the "Back-End Cancellation Consideration"), less any applicable withholding taxes, including any Dutch dividend withholding tax (dividendbelasting) due in respect of the Back-End Cancellation Consideration. As a result of the Back-End Merger and the Back-End Cancellation, Purchaser indirectly acquired an additional 1,982,906 Common Shares (representing approximately 2.61% of the Issuer's outstanding Common Shares based upon the 75,867,199 Common Shares outstanding as of December 29, 2025, according to the Depositary). No Common Shares remain outstanding following the consummation of the Back-End Merger and the Back-End Cancellation."

The information in Item 5(a) of this Amendment No. 1 is incorporated herein by reference.

Except as described in this Amendment No. 1, there were no other transactions with respect to Common Shares effected during the past 60 days by the Reporting Persons, or to the knowledge of the Reporting Persons, any of the persons listed in Schedule I of the Offer to Purchase.

To the best knowledge of the Reporting Persons, no other person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Shares beneficially owned by the Reporting Persons.

The information in Item 5(a) of this Amendment No. 1 is incorporated herein by reference.