Multiple law firms have announced a class-action lawsuit against Gossamer Bio, Inc. (NASDAQ: GOSS) on behalf of investors who purchased securities between June 16, 2025, and February 20, 2026, alleging violations of federal securities laws.
"According to the lawsuit, defendants provided overwhelmingly positive statements to investors while, at the same time, disseminating false and misleading statements and/or concealing material adverse facts concerning the study design for Gossamer’s Phase 3 PROSERA study," a press release from Rosen Law Firm stated.
The lawsuit follows the company’s February 23, 2026, announcement that its PROSERA study for seralutinib in treating pulmonary arterial hypertension failed to meet its primary endpoint. The news sent Gossamer’s stock price down 80% in a single day. The company also disclosed on April 9, 2026, that it was not in compliance with the Nasdaq’s minimum bid price requirement of $1.00 per share.
Investors who purchased Gossamer securities during the class period have until June 1, 2026, to file a motion to serve as lead plaintiff. The litigation seeks to recover damages for investors who suffered losses following the announcement of the trial results.
The core of the complaint centers on allegations that Gossamer failed to disclose critical flaws in its Phase 3 PROSERA trial. Specifically, the lawsuit claims the company did not properly control for a significant placebo response observed at its Latin American testing sites.
The complaint alleges that management had previously highlighted the success of a competitor's trial in Latin America to assure investors of its own strategy, stating that Gossamer had recruited "more patients coming from those same geographies and same sites." However, the lawsuit contends that patients at these sites were heavily pre-treated and performing unusually well on placebo, which materially compromised the trial's ability to show a statistically significant treatment effect.
The market’s reaction to the trial failure was severe, erasing hundreds of millions in market capitalization. The 80% stock drop on February 23, 2026, reflected a complete loss of confidence in seralutinib's multi-billion dollar potential, which the company had previously emphasized to investors.
Compounding the company's troubles, Gossamer received a notice from the Nasdaq Stock Market on April 9, 2026, indicating that its common stock had failed to maintain a minimum bid price of $1.00 for 30 consecutive business days. While the company has a grace period to regain compliance, the notice puts it at risk of being delisted from the exchange, which would further impair its stock's liquidity and value.
The lawsuit represents a significant challenge for Gossamer as it navigates the fallout from the failed study. For investors, the June 1, 2026, deadline is the next key date as law firms seek a lead plaintiff to direct the litigation.
This article is for informational purposes only and does not constitute investment advice.
