Regeneron faces securities lawsuit over clinical trial misstatements
SAN FRANCISCO, Sept. 1, 2026 /CourierPR/ -- Regeneron Pharmaceuticals faces a significant legal challenge after a securities class action lawsuit was filed over the company's handling of a Phase 3 clinical trial. The lawsuit, which seeks to represent investors who purchased or held Regeneron common stock between August 1, 2025, and May 15, 2026, alleges that the company made false and misleading statements about the trial's progress.
According to Hagens Berman Sobol Shapiro LLP, a national shareholder rights firm, Regeneron's repeated optimistic statements about the trial's primary endpoint—progression-free survival—were misleading. The firm argues that the company failed to disclose critical information to investors regarding the trial's statistical assumptions and the likelihood of achieving the primary endpoint.
"The litigation is focused on the propriety of Regeneron's repeated optimism about the state of the ongoing Phase 3 trial of Fianlimab in combination with Libtayo as a first-line treatment for metastatic or locally advanced melanoma," said Reed Kathrein, a partner at Hagens Berman leading the investigation. "Regeneron assured investors of their confidence in the trial's primary endpoint even as events were slowing down."
The lawsuit alleges that Regeneron's preliminary statistical assumptions were flawed, and that the active treatment arm was not achieving meaningful differentiation over standard therapies. Regeneron's management, according to the complaint, did not inform investors that achieving the primary endpoint was unlikely.
The truth began to emerge on April 29, 2026, when Regeneron announced that it would alter the trial protocol. The company stated that the primary analysis of progression-free survival would now consider all patients enrolled in the study with a minimum follow-up of six months. This change came as the "underlying PFS benefit may be insufficient to show statistical significance," according to a prominent analyst.
On May 12, 2026, Regeneron admitted that the decision to alter the trial protocol was made in response to slow event rates, which had been ongoing for nearly six months. The company submitted the amended protocol to global regulatory authorities in November or December 2025. The final blow came on May 15, 2026, when Regeneron reported that the trial did not reach statistical significance for the primary endpoint of improvement in progression-free survival.
"We're focused on whether Regeneron altered the trial protocol without timely telling investors to intentionally mislead them because the defendants knew so-called blockbuster potential for the combination wasn't really there," Kathrein stated.
Hagens Berman is urging Regeneron investors with substantial losses to submit their claims now. The firm is also seeking individuals who may have relevant information to contact its attorneys. The lead plaintiff deadline is September 14, 2026.