Lantheus Holdings, Inc.

Since the filing of the Definitive Proxy Statement, three complaints have been filed against the Company and certain members of the Board in connection with the Merger. Two such complaints were filed in the Supreme Court of the State of New York, County of New York: Hamilton v. Lantheus Holdings, Inc., et al., Index No. 655291/2026, filed on September 16, 2026, and McDaniels v. Lantheus Holdings, Inc., et al., Index No. 655281/2026, filed on September 16, 2026, and one was filed in the Superior Court of the Commonwealth of Massachusetts, Middlesex County: Garfield v. Lantheus Holdings, Inc., et al., Civil Docket No. 2681CV02581, filed on September 25, 2026 (collectively, the “Complaints”). The Complaints generally allege, among other things, that the Definitive Proxy Statement omits or misrepresents certain information concerning the Company’s financial projections, the financial analyses performed by Morgan Stanley in connection with its fairness opinion, and potential conflicts of interest involving Company insiders, including information concerning potential post-closing employment or retention. The Complaints assert claims under state common law and seek, among other things, to enjoin consummation of the Merger unless and until certain additional information is disclosed.

In addition to the Complaints, as of September 30, 2026, the Company has received sixteen demand letters from purported stockholders of the Company, including two that attached a draft complaint (collectively, the “Demand Letters”). The Demand Letters generally seek disclosure of certain information allegedly omitted from the preliminary proxy statement and/or Definitive Proxy Statement. Additional demand letters or lawsuits may be received by or filed against the Company, members of the Board, Parent and/or Merger Sub in connection with the Merger or the Definitive Proxy Statement. If additional demand letters are received or complaints are filed, the Company will not necessarily announce such additional demands or filings.

Solely to avoid the costs, burden, nuisance and uncertainties inherent in litigation and to allow the Company’s stockholders to vote on the Merger at the Special Meeting, without admitting any liability or wrongdoing, the Company is providing additional disclosures related to information contained in the Definitive Proxy Statement (the “Supplemental Disclosures”). The Supplemental Disclosures are set forth below and should be read in conjunction with the Definitive Proxy Statement.

The Company denies that the Definitive Proxy Statement is deficient in any respect and that the Supplemental Disclosures are material or required. The Company believes that the Complaints and the Demand Letters are without merit and that no further disclosure is required to supplement the Definitive Proxy Statement under applicable laws. Nothing in this Current Report on Form 8-K will be deemed an admission of the legal necessity or materiality under any applicable laws for any of the disclosures set forth herein.