Regeneron Sued Over Failed Melanoma Trial, $11B Market Cap Loss
San Francisco – September 10, 2026 -- Hagens Berman Sobol Shapiro LLP has filed a securities class action against Regeneron Pharmaceuticals (NASDAQ: REGN) after the failure of a Phase 3 melanoma trial wiped out $11 billion in market capitalization. The suit covers investors who purchased Regeneron shares between August 1, 2025, and May 15, 2026, with a lead plaintiff deadline set for September 14, 2026.
Regeneron's Fianlimab-Libtayo combination failed to hit its primary endpoint
The complaint centers on Regeneron's Phase 3 trial testing Fianlimab combined with Libtayo as a first-line treatment for metastatic or locally advanced melanoma, a therapy management repeatedly called a "potential blockbuster." On May 15, 2026, Regeneron disclosed the trial did not reach statistical significance on its primary endpoint of progression-free survival.