Key Takeaways:
Gossamer Bio, Inc. (NASDAQ: GOSS) faces a securities class action lawsuit after the company’s stock plummeted 80.3% on February 23, 2026, following the announcement that its Phase 3 PROSERA study for seralutinib failed to meet its primary endpoint.
"We're focused on whether Gossamer may have misled investors about the PROSERA trial design, including patient entry criteria, as alleged in the pending lawsuit," said Reed Kathrein, a partner at Hagens Berman, one of several firms that has filed a complaint.
The lawsuit, representing investors who purchased shares between June 16, 2025, and February 20, 2026, alleges the company concealed design flaws in the trial. On the day of the announcement, Gossamer's stock fell $1.71 to close at $0.42. The company later disclosed on April 9, 2026, that it no longer met the minimum $1 bid price for continued listing on the Nasdaq.
The core of the complaint is that Gossamer knew or recklessly disregarded that an "outsize placebo response" at its Latin American sites would dilute the study's results, rendering its positive statements during the class period misleading. The deadline for investors to move the court to be appointed lead plaintiff is June 1, 2026.
According to the complaints filed by multiple law firms, including Rosen Law Firm and Bronstein, Gewirtz & Grossman, Gossamer failed to disclose that patients at its Latin American study sites were a "heavily-treated lower-risk population." This group allegedly performed particularly well on the placebo, which the company’s management said "materially diluted" the overall treatment effect and "compressed the pool placebo-adjusted difference."
The allegations stand in contrast to the company's previous statements. In November 2025, Gossamer management had pointed to the successful Merck STELLAR study, assuring investors that "we have actually more patients coming from those same geographies and same sites" in Latin America, which had been a high-performing region in the Merck trial. The company had previously touted seralutinib as a potential multi-billion-dollar opportunity.
The 80% single-day collapse in value has erased the majority of Gossamer's market capitalization, putting the future of its pipeline and ability to raise capital into question. The stock's failure to maintain the minimum bid price requirement for Nasdaq listing adds further pressure. Investors will now watch for the court's decision on the lead plaintiff and the company's formal response to the class action allegations.
This article is for informational purposes only and does not constitute investment advice.
