Regeneron Pharmaceuticals faces a securities class action lawsuit over alleged misstatements and omissions concerning a Phase 3 trial of Fianlimab combined with Libtayo for melanoma. The case, Cheatham v. Regeneron Pharmaceuticals, Inc., No. 26-cv-06026, is pending in the U.S. District Court for the Southern District of New York. Robbins Geller Rudman & Dowd LLP says investors who purchased or acquired Regeneron common stock between Aug. 1, 2025, and May 15, 2026, may seek appointment as lead plaintiff by Sept. 14, 2026. The complaint alleges that Regeneron and certain top executives overstated the study's prospects, downplayed the impact of slowing event rates, relied on flawed preliminary statistical assumptions and failed to disclose that the treatment arm was not achieving meaningful differentiation from standard therapies. Regeneron disclosed on April 29 that the study had been altered to expand the number of patients eligible for progression-free-survival analysis. After the company said on May 15 that the trial failed to reach statistical significance for its primary endpoint, Regeneron shares fell nearly 10%, according to the complaint; the stock had earlier declined more than 6% after the April disclosure. The announcement follows an investigation previously described by Hagens Berman, which said the trial failure erased $11 billion in market capitalization.