A securities class action has been filed against Regeneron Pharmaceuticals, Inc. (REGN) on behalf of all investors who purchased or otherwise acquired Regeneron common stock between August 1, 2025 through May 15, 2026. This case has been filed in the USDC – SDNY.
The complaint alleges Regeneron provided investors with material information concerning Regeneron’s Phase III clinical trial of Fianlimab, a LAG-3 inhibitor, in combination with cemiplimab, a PD-1 inhibitor, as a first-line treatment for metastatic or locally advanced melanoma (the “Phase III Fianlimab-Libtayo Study”). Regeneron’s statements included, among other things, overwhelming confidence in the drug combination’s potential for success and a mischaracterization of the additional structural risk imposed on the study by the prolonged slowdown in event accruals.
Regeneron repeatedly and falsely characterized this slowdown as a likely positive development that reflected the durable efficacy of the active treatment arms, while knowingly or recklessly disregarding that the actual risk of clinical failure had dramatically increased due to the nature of the delayRegeneron’s representations regarding the nature and impact of the slowdown mischaracterized the actual risk of failure that the study was facing.
Regardless, Regeneron provided overwhelmingly positive statements to investors while, at the same time, disseminating materially false and misleading statements and/or concealing material adverse facts concerning the true state of Regeneron’s Phase III Fianlimab-Libtayo Study; notably, that its preliminary statistical assumptions were fundamentally flawed, that the active treatment arm was failing to achieve meaningful clinical differentiation over standard therapies, and that the trial would ultimately fail to reach statistical significance on its primary endpoint even without overperformance of the control arm. Such statements absent these material facts caused Plaintiff and other shareholders to purchase Regeneron’s securities at artificially inflated prices.
Shareholders began to question the veracity of Regeneron’s public statements on April 29, 2026, during Regeneron’s first quarter earnings call. In pertinent part, Regeneron disclosed the Phase III Fianlimab-Libtayo Study had been altered, expanding the number of patients in the study eligible for “analysis of progression-free survival.”
Investors and analysts reacted immediately to Regeneron’s revelation. The price of Regeneron’s common stock declined dramatically. From a closing market price of $731.77 per share on April 28, 2026, Regeneron’s stock price fell to $686.36 per share on April 29, 2026, a decline of about 6.2% in the span of just a single day.
Notwithstanding the April 29 disclosures, Regeneron and the Individual Defendants continued to mislead investors. Regeneron continued to develop the false impression that they possessed reliable information pertaining to the likelihood of the Phase III Fianlimab-Libtayo Study to achieve its primary endpoint and the overall risk profile of the study. Despite being forced to issue a last-minute amendment to the study’s protocol in order to increase the acceptable patient pool for consideration of the primary endpoint analysis, Regeneron continued to suggest that this crawling pace with which the study was reaching event accruals necessary for comparison was a positive development absent the control group doing “something miraculous” to offset the treatment arm’s performance.
The full truth finally emerged after-market on May 15, 2026, when Regeneron issued a press release announcing that the “Phase 3 Trial of Fianlimab . . . did not reach statistical significance for the primary endpoint of improvement in progression-free survival (PFS).” Investors and analysts again reacted promptly to Regeneron’s revelation. The price of Regeneron’s common stock declined even further. From a closing market price of $698.25 per share on May 15, 2026, Regeneron’s stock price fell to $629.68 per share on May 18, 2026, a decline of about 9.8% in the span of one day.