Lantheus Holdings, Inc.

Item 8.01 Other Events. As previously disclosed, on August 3, 2026, Lantheus Holdings, Inc., a Delaware corporation (“Lantheus” or the “Company”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) by and among the Company, Curium US Holdings LLC, a Delaware limited liability company (“Parent”), and Coco Merger Sub Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), pursuant to which, subject to the terms and conditions set forth therein, including the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”), Merger Sub will merge with and into the Company (the “Merger”), with the Company surviving the Merger as a wholly owned subsidiary of Parent. As part of the parties’ continuing cooperation with the regulatory review of the Merger, on September 17, 2026, Parent, as the acquiring party, in consultation with the Company, voluntarily withdrew its pre-merger Notification and Report Form filed pursuant to the HSR Act, in order to provide the Federal Trade Commission (the “FTC”) with additional time to review the Merger. Parent resubmitted its pre-merger Notification and Report Form on September 21, 2026, commencing a new 30-day waiting period under the HSR Act, which will expire on October 21, 2026, at 11:59 p.m., Eastern Time, unless terminated earlier or extended. This statutory waiting period may be extended if the FTC issues a request for additional information and documentary material. Withdrawing and refiling pre-merger notifications is a routine procedure in order to provide additional time for antitrust review of certain transactions. The Company and Parent continue to work constructively with the FTC staff in the FTC’s review of the Merger and continue to expect to consummate the Merger in the first half of 2027, subject to the receipt of required regulatory approvals, the adoption of the Merger Agreement by the Company’s stockholders, and the satisfaction or waiver of other customary closing conditions. Additional Information and Where to Find It In connection with the proposed acquisition of the Company by Parent, the Company filed a definitive proxy statement with the Securities and Exchange Commission (the “SEC”) on September 8, 2026. This document is not a substitute for the definitive proxy statement or any other document that may be filed by the Company with the SEC. THE COMPANY’S STOCKHOLDERS AND INVESTORS ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT IN ITS ENTIRETY AND ANY OTHER DOCUMENTS FILED BY EACH OF PARENT AND THE COMPANY WITH THE SEC IN CONNECTION WITH THE PROPOSED ACQUISITION OR INCORPORATED BY REFERENCE THEREIN BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED ACQUISITION AND THE PARTIES TO THE PROPOSED ACQUISITION. Investors and security holders are able to obtain a free copy of the proxy statement and such other documents containing important information about the Company and Parent through the website maintained by the SEC at www.sec.gov. The Company makes available free of charge at its website at https://investor.lantheus.com/ copies of materials it files with, or furnishes to, the SEC. Participants in the Solicitation The Company, Parent and certain of their respective directors, executive officers and employees may be deemed to be participants in the solicitation of proxies from the stockholders of the Company in connection with the proposed acquisition. Information regarding the Company’s directors and executive officers is contained in the definitive proxy statement. To the extent holdings of the Company’s securities by its directors or executive officers have changed since the amounts set forth in the definitive proxy statement, such changes have been or will be reflected on Initial Statements of Beneficial Ownership of Securities on Form 3 or Statements of Changes in Beneficial Ownership of Securities on Form 4 filed with the SEC. These documents may be obtained free of charge from the SEC’s website at www.sec.gov and the Company’s website at https://investor.lantheus.com/. The contents of the websites referenced herein are not deemed to be incorporated by reference into the proxy statement.