Regeneron investors who purchased or acquired the company’s common stock from Aug. 1, 2025, through May 15, 2026, have until Sept. 14, 2026, to seek appointment as lead plaintiff in a securities class action filed in the U.S. District Court for the Southern District of New York. The case, Cheatham v. Regeneron Pharmaceuticals, Inc., No. 26-cv-06026, names Regeneron and certain top executives and alleges violations of the Securities Exchange Act of 1934. The complaint centers on disclosures about the Phase III Fianlimab-Libtayo study in melanoma, which failed to achieve statistical significance for its primary endpoint of progression-free survival. Regeneron disclosed a study alteration on April 29, 2026, and reported the failed trial after market close on May 15; the complaint says the stock fell more than 6% after the April disclosure and nearly 10% after the May announcement, while an earlier investor announcement attributed an $11 billion market-capitalization loss to the failure. Robbins Geller Rudman & Dowd LLP is soliciting investors seeking lead-plaintiff status, while Hagens Berman has separately announced an investigation and earlier litigation-related claims concerning the disclosures.