Regeneron Pharmaceuticals faces securities class-action litigation from Hagens Berman Sobol Shapiro LLP and a separate announcement from Pomerantz LLP over disclosures about its Phase 3 Fianlimab-Libtayo study for melanoma. Hagens Berman says the trial failure and related disclosures erased about $11 billion in market value. The firm alleges Regeneron failed to disclose flawed preliminary statistical assumptions, limited differentiation from standard therapies and the reduced likelihood of reaching the study’s progression-free-survival endpoint. Regeneron disclosed on April 29, 2026, that it had changed the trial protocol because of slowing event rates, acknowledged on May 12 that the change had been submitted to global regulators months earlier, and reported on May 15 that the trial did not achieve statistical significance for its primary endpoint. Existing litigation materials from Pomerantz cited share declines of $45.41, or 6.21%, on April 29 and $68.57, or 9.82%, to $629.68 on May 16. The proposed class period runs from August 1, 2025, through May 15, 2026, and the lead-plaintiff deadline is September 14, 2026.