Regeneron faces securities lawsuit after $11 billion trial wipeout

Regeneron Pharmaceuticals faces a securities class action after its melanoma trial failed, wiping out $11 billion in market value and sending shares down 13.95 percent.

"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," Reed Kathrein, partner at Hagens Berman, said.

The lawsuit covers investors who bought Regeneron (NASDAQ: REGN) common stock between Aug. 1, 2025 and May 15, 2026. Shares fell from a class-period high of $731.77 on April 28, 2026 to $629.68 after the May 15 announcement, a $102.09 per-share decline. The complaint alleges Regeneron and management made false and misleading statements about the Phase 3 Fianlimab-Libtayo study for metastatic or locally advanced melanoma, whose primary endpoint was progression-free survival.

The lead plaintiff deadline is Sept. 14, 2026. The case was filed in the US District Court for the Southern District of New York under the Private Securities Litigation Reform Act of 1995.

The litigation centers on Regeneron's repeated optimism about the study, which the company characterized as a "potential blockbuster." The complaint alleges the company failed to disclose that the study's preliminary statistical assumptions were flawed, the active treatment arm was not achieving meaningful differentiation over standard therapies, and achievement of the primary endpoint was unlikely.

The truth began to emerge April 29, 2026, when Regeneron said it would alter the trial protocol so the primary analysis of progression-free survival would consider all enrolled patients with a minimum follow-up of six months. On May 12, Regeneron admitted the change was made in response to "slow event rates" and had been submitted to global regulators in November and December. Three days later, Regeneron reported the trial "did not reach statistical significance" on its primary endpoint.

Ryan Crowe, Regeneron's senior vice president of investor relations and strategic analysis, is named as an individual defendant. The complaint identifies investor-facing presentations in which Crowe discussed the study, prior Phase 1 results showing a 57 percent objective response rate and 24-month median progression-free survival, and the significance of slowing event accrual.

The action asserts claims under Sections 10(b) and 20(a) of the Securities Exchange Act and Rule 10b-5. Multiple firms, including Hagens Berman, Levi & Korsinsky, Pomerantz and Bronstein Gewirtz & Grossman, are soliciting investors to seek lead plaintiff appointment.

The lawsuit adds legal and reputational risk for Regeneron as it weighs potential settlement costs and the loss of a pipeline candidate once expected to drive growth. Investors will watch the Sept. 14 lead plaintiff deadline and any subsequent court rulings on the adequacy of the company's trial disclosures.

This article is for informational purposes only and does not constitute investment advice.