Hagens Berman said the suit covers investors who bought Regeneron shares from Aug. 1, 2025, to May 15, 2026, after the company's Phase 3 Fianlimab-Libtayo study missed its main progression-free survival goal.
Regeneron Pharmaceuticals is facing a securities class action after disclosing that its Phase 3 clinical trial of Fianlimab in combination with Libtayo as a first-line treatment for metastatic or locally advanced melanoma failed to reach statistical significance on its primary endpoint of improvement in progression-free survival (PFS), a measure of how long patients live without disease worsening. Hagens Berman Sobol Shapiro LLP said the May 15, 2026 disclosure helped trigger a sharp share-price decline and an $11 billion market-cap loss, and the proposed class covers investors who bought or otherwise acquired Regeneron common stock between Aug. 1, 2025 and May 15, 2026, with a lead plaintiff deadline of Sept. 14, 2026. The complaint alleges Regeneron and its management misled investors by promoting the study as a "potential blockbuster" while failing to disclose allegedly flawed statistical assumptions, weak differentiation versus standard therapies and the low likelihood of meeting the main goal even as event rates slowed. The release also points to Regeneron's April 29 protocol change and its May 12 statement that the change had been made nearly six months earlier because of "slow event rates," while Hagens Berman said it is investigating and urged investors and potential whistleblowers to come forward, including through the SEC (U.S. securities regulator) Whistleblower program.