Lantheus Holdings, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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2026 Notice of Annual Meeting of Stockholders & Proxy Statement ~7M patient lives impacted in 20251

Lantheus 2026 Proxy Statement

Dear Valued Shareholder,

We cordially invite you to attend Lantheus Holdings, Inc.’s 2026 Annual Meeting of Shareholders, to be held on Thursday, April 30, 2026 at 9:00 a.m. (Eastern Time) in the North Bldg. Cafe at the Lantheus Bedford Office, 201 Burlington Rd., Bedford, MA 01730, United States. The meeting will also be hosted in virtual format via the Internet. You will be able to attend the meeting virtually and vote and submit questions by visiting and registering at www.proxydocs.com/LNTH.

The Notice of Internet Availability of Proxy Materials and the Proxy Statement that follow describe the business to be conducted at the meeting.

Your vote is important. We encourage you to vote by proxy in advance of the Annual Meeting, whether or not you plan to attend the meeting. On behalf of the Board of Directors, thank you for your continued investment in our company.

Sincerely,

Mary Anne Heino

Executive Chairperson and Chief Executive Officer

Lantheus 2026 Proxy Statement

Message from our CEO March 20, 2026 Dear Valued Shareholder, 2025 was a year of decisive action at Lantheus—one in which we strengthened our leadership in PET diagnostics, advanced and expanded our portfolio and positioned the company for its next phase of growth and value creation. These actions were guided by our Purpose—to Find, Fight and Follow disease to deliver better patient outcomes—which continues to anchor every strategic and operational decision we make. In 2025, our products impacted the lives of nearly seven million patients and their families, a powerful reminder of the real-world importance of diagnostics and the impact our teams have every day. As previously disclosed, I am currently serving as Executive Chairperson and Interim Chief Executive Officer while the Board of Directors conducts a search for Lantheus’ next CEO. My focus during this period is clear: to ensure continuity of leadership, disciplined execution and a seamless transition for the company. The search process is progressing well, and we remain fully focused on executing our strategy during this important time. ~7M patients and their families impacted in 2025, a powerful reminder of the real-world importance of diagnostics and the impact our teams have every day. Sharpening Our Strategic Focus Building on the actions we took in 2025, we are now focused on innovative PET radiodiagnostics where we have differentiated capabilities, deep customer relationships and clear line of sight to near- and mid-term value creation. At the same time, we are taking purposeful steps to optimize the value of our broader portfolio. In 2025, we closed two complementary transactions that diversified, and will accelerate, our near-term revenue streams. With our acquisition of Life Molecular Imaging (now known as Lantheus Biosciences), we added Neuraceq®, a beta amyloid-targeted PET radiodiagnostic. Neuraceq serves as the commercial cornerstone of our Alzheimer’s disease portfolio. This acquisition also provides us with differentiated R&D capabilities and an established international footprint, including a neurology commercial infrastructure.

Lantheus 2026 Proxy Statement

With our acquisition of Evergreen Theragnostics, we expanded our oncology radiodiagnostic pipeline with OCTEVY™, a registrational-stage PET diagnostic agent for neuroendocrine tumors (NETs), and we added scalable manufacturing capabilities that enhance our ability to meet the complex demands of radiopharmaceutical development and production. In parallel, we completed the divestiture of our legacy SPECT business, effective January 1, 2026. While these products were foundational to Lantheus’ longstanding reputation in nuclear medicine, this decision reflects our commitment to aligning capital, talent and operational resources with areas where we see the greatest opportunity for sustainable growth over time. Today, our broad portfolio reflects our deep history and expertise in nuclear medicine, allowing us to provide customers with a range of products to address diverse clinical needs. Operational Execution In 2025, we maintained our leadership position in PSMA PET imaging in the U.S. with PYLARIFY® in a competitive marketplace. Our 2025 performance reflects our broad customer base and the clinical value of PYLARIFY. Neuraceq exited 2025 as the fastest-growing amyloid PET agent and the second most utilized in the U.S., driven by strong underlying demand and commercial execution. By leveraging our manufacturing network, distribution capabilities and commercial infrastructure, we are expanding access to amyloid PET imaging as its role in Alzheimer’s care continues to grow. DEFINITY® continued to deliver steady, volume-driven growth and remains a durable contributor to our portfolio. DEFINITY’s performance reflects its enduring clinical value and the operational excellence that underpins our reputation for reliability with our customers. Advancing Our Late-Stage Pipeline In 2026, we are taking purposeful steps to advance multiple late-stage radiodiagnostic assets toward regulatory milestones while ensuring fit-for-purpose commercial launches. PYLARIFY TruVu™, our new PSMA PET formulation, received FDA approval [March X] and is expected to reinforce our leadership in prostate cancer imaging by improving manufacturing efficiency and supply availability. We are preparing for a disciplined, regionally phased launch beginning in the fourth quarter of 2026. In neuroendocrine tumors, PNT2003, our radioequivalent version of LUTATHERA® for gastroenteropancreatic neuroendocrine tumors (GEPNETs), received tentative approval for its Abbreviated New Drug Application (ANDA) in February 2026, marking an important step toward making this treatment option available to patients pending final FDA approval. OCTEVY, our gallium-based PET diagnostic for neuroendocrine tumors, has a PDUFA date of March 29, and if approved, we expect to launch OCTEVY as the only neuroendocrine PET agent with Transitional Pass-Through reimbursement in a well-established NET imaging market. MK6240, our tau-targeted PET radiodiagnostic for Alzheimer’s disease, is advancing toward its August 13 PDUFA date. MK6240 is currently the most widely used tau imaging agent in late-stage Alzheimer’s diseasemodifying therapy development, serving as the imaging agent for treatment eligibility across numerous ongoing clinical programs. During 2025, we initiated a comprehensive, ongoing review of our pipeline as part of our disciplined approach to portfolio management. While we continue to advance select assets with near-term potential, we have made the decision to pursue value-maximizing alternatives for certain radiotherapeutic programs. This enables us to focus investment where we see the greatest opportunity, while ensuring that the value of our broader portfolio is thoughtfully managed for the benefit of our shareholders.

Lantheus 2026 Proxy Statement

Operating Our Business Responsibly Beyond our financial and operational progress, Lantheus remains committed to operating responsibly and making a positive impact in the communities we serve. In 2025, we continued to support charitable initiatives aligned with our Purpose and advanced programs that reflect our commitment to patients, communities, and employees. At Lantheus, our people are the foundation of our success. During 2025, we undertook significant efforts to bring together three organizations into a newly integrated and optimized Lantheus operating model, aligning teams, processes and culture to support collaboration and drive sustained performance. We remain focused on fostering an inclusive, growth-oriented culture that places patients and people at the center of everything we do. Driving Sustainable Value With a diversified portfolio, strong operational execution and a robust late-stage pipeline with meaningful catalysts, Lantheus is well positioned to support sustained growth and long-term value creation. 2026 brings important regulatory decisions and the potential to advance new products to patients. We see this year as one of disciplined execution, operational readiness and targeted investment to support future growth. As we look to the remainder of 2026, our priorities are clear: • Maintain market leadership in PSMA PET by sustaining PYLARIFY volume growth • Ensure a seamless transition to our new PSMA PET formulation beginning in 4Q 2026 • Increase momentum for Neuraceq by expanding our manufacturing footprint and driving deeper penetration in existing accounts and accounts where a strong PYLARIFY relationship already exists • Advance our assets currently under FDA review through approval milestones and effect fit-for-purpose launch activities for those assets that offer the earliest, and best, revenue return • Selectively develop other pipeline assets toward key development decision points • Allocate capital with discipline, prioritizing radiodiagnostics, optimizing the value of our radiotherapeutic pipeline, and maintaining financial flexibility while committing to a leveraged P&L that delivers value to our shareholders I want to thank our employees, Board of Directors, customers, partners and you—our shareholders—for your continued trust and support. With a clear strategy and strong leadership team in place, we remain focused on disciplined execution as the Board progresses its CEO search and prepares for a seamless leadership transition. Together, we will continue to Go Further for patients and deliver durable value for our shareholders. Sincerely, Mary Anne Heino Chief Executive Officer Executive Chair of the Board

Lantheus 2026 Proxy Statement

Notice of Annual Meeting of Shareholders