Regeneron Faces Securities Class Action Over Failed Clinical Trial

SAN FRANCISCO, Sept. 7, 2026 /CourierPR/ -- Regeneron Pharmaceuticals, Inc., a leading biotechnology company, is facing a securities class action lawsuit after the unexpected failure of a Phase 3 clinical trial. The lawsuit, filed by Hagens Berman Sobol Shapiro LLP, alleges that the company made false and misleading statements to investors during the period from August 1, 2025, to May 15, 2026.

The primary endpoint of the trial, progression-free survival (PFS), was expected to show significant improvement for Regeneron's therapy in combination with Libtayo as a first-line treatment for metastatic or locally advanced melanoma. However, on May 15, 2026, Regeneron announced that the trial did not reach statistical significance, leading to a sharp decline in the company's stock price and a $11 billion market cap loss.

According to the lawsuit, Regeneron and its management made repeated assurances of confidence in the trial's success, despite internal concerns. The company’s management stated that slowing event rates were due to the test arms performing well. However, the truth began to emerge on April 29, 2026, when Regeneron revealed plans to alter the trial protocol to consider all patients with a minimum follow-up of six months. This decision was reportedly made to avoid statistical insignificance, as the underlying PFS benefit was insufficient.

Prior to this, on May 12, 2026, Regeneron admitted that the protocol change was made in response to slow event rates, which had occurred nearly six months earlier. The lawsuit accuses Regeneron and its management of failing to disclose critical information about the trial's preliminary statistical assumptions and the lack of meaningful differentiation from standard therapies.

Hagens Berman Sobol Shapiro LLP is urging investors who purchased Regeneron shares between August 1, 2025, and May 15, 2026, and suffered substantial losses to submit their claims. The firm is also seeking to identify individuals who may have information that can assist in the investigation. The deadline for filing as a lead plaintiff is September 14, 2026.

The complaint highlights the company’s repeated optimism about the trial's success, despite internal indications of potential failure. The lawsuit argues that Regeneron and its management intentionally misled investors by not disclosing the true state of the trial and the underlying issues that led to the protocol changes.

Regeneron Pharmaceuticals, Inc., has been at the forefront of developing innovative cancer therapies, and the failure of this trial could have significant implications for the company's future. The lawsuit aims to hold the company accountable for its alleged false statements and misrepresentations to investors.