Investor Notice: Robbins LLP Informs Investors of the Regeneron Pharmaceuticals, Inc. Class Action Lawsuit

SAN DIEGO--(BUSINESS WIRE)--Robbins LLP informs stockholders that a class action was filed on behalf of investors who purchased or otherwise acquired Regeneron Therapeutics, Inc. (NASDAQ: REGN) from August 1, 2025 to May 15, 2026. Regeneron is a pharmaceutical company that discovers, invents, develops, manufactures, tests, and commercializes medicines to treat various disorders worldwide.

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The Allegations: Robbins LLP is Investigating Allegations that Regeneron Therapeutics, Inc. (REGN) Misled Investors Regarding the Viability of its Phase III Fianlimab-Libtayo Study

According to the complaint, during the relevant period, Regeneron was investigating Fianlimab, a human monoclonal antibody targeting the LAG-3 immune checkpoint receptor on T-cells. Fianlimab was pertinently being tested in combination with Libtayo in a phase 3 study to determine whether the drug combination could serve as a first-line treatment for advanced melanoma (the “Phase III Fianlimab-Libtayo Study”). The study had commenced enrollment in mid-2022.

Plaintiff alleges that defendants provided overwhelmingly positive statements to investors while, at the same time, concealing the true state of Regeneron’s Phase III Fianlimab Libtayo Study; notably, that (i) its preliminary statistical assumptions were fundamentally flawed; (ii) the active treatment arm was failing to achieve meaningful clinical differentiation over standard therapies; and (iii) the trial would ultimately fail to reach statistical significance on its primary endpoint even without overperformance of the control arm.

Plaintiff alleges that April 29, 2026, during Regeneron’s first quarter earnings call, defendants 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.” On this news, the price of Regeneron’s common stock declined from a closing market price of $731.77 per share on April 28, 2026, to $686.36 per share on April 29, 2026, a decline of about 6.2% in the span of just a single day. Then, after-market on May 15, 2026, Regeneron announced that the “Phase 3 Trial of Fianlimab . . . did not reach statistical significance for the primary endpoint of improvement in progression-free survival (PFS).” On this news, the price of Regeneron’s common stock declined from $698.25 per share on May 15, 2026, to $629.68 per share on May 18, 2026, a decline of about 9.8% in the span of one day.

What Now: You may be eligible to participate in the class action against Regeneron Therapeutics, Inc. Shareholders who wish to serve as lead plaintiff for the class should contact Robbins LLP. The lead plaintiff is a representative party who acts on behalf of other class members in directing the litigation. You do not have to participate in the case to be eligible for a recovery. If you choose to take no action, you can remain an absent class member. For more information, click here.

All representation is on a contingency fee basis. Shareholders pay no fees or expenses.

About Robbins LLP: A recognized leader in shareholder rights litigation, Robbins LLP has helped restore more than $1 billion in value to shareholders, secured some of the largest recoveries in shareholder derivative litigation history, and achieved governance reforms at over 400 Fortune 1000 companies.

"Behind everything we do is the belief that companies should be governed responsibly, fiduciaries should be held accountable, and shareholders deserve transparency and fairness," said Brian J. Robbins, Founding Partner of Robbins LLP.

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