Overview

A class action lawsuit has been filed against Gossamer Bio, Inc. (“Gossamer” or the “Company”) (NASDAQ : GOSS) and the Company’s Chief Executive Officer (“CEO”) (collectively, “Defendants”), alleging violations of the federal securities laws. The Gossamer lawsuit is brought on behalf of all persons and entities who purchased or otherwise acquired Gossamer securities between June 16, 2025, and February 20, 2026, inclusive (the “Class Period”). Investors have until June 1, 2026, to seek appointment as lead plaintiff of the Gossamer class action lawsuit.

Gossamer is a clinical stage biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary hypertension (PH) associated with lung disease.

The complaint alleges that throughout the Class Period, Defendants represented that the Company’s Phase 3 PROSERA study evaluating seralutinib was well-designed and likely to achieve its primary endpoint, expressing confidence in patient selection and the study’s execution. The complaint further alleges that, in reality, Defendants failed to disclose issues relating to patient populations and unusually strong placebo responses at Latin American clinical sites. These undisclosed factors materially increased the risk that the trial would fail to meet its primary endpoint.

The truth was revealed on February 23, 2026, when Gossamer published a press release and hosted a Special Call announcing the topline results from its Phase 3 PROSERA study. The Company disclosed it was “disappointed to have narrowly missed the stringent prespecified statistical threshold for our primary endpoint.”  The Company attributed the failure in part to unexpectedly strong placebo responses, especially in Latin America, which reduced the observed treatment effect.

On this news, the price of Gossamer’s common stock plummeted, falling from a market price of $2.13 per share on February 20, 2026, to $0.42 per share on February 23, 2025, a decline of approximately 80%. 

Analysts expressed surprise and concern at the Company’s primary endpoint miss. In particular, on February 24, 2026, Wedbush published a report downgrading Gossamer stock and decreasing the Company’s price target from $6 to $1.

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If you purchased or otherwise acquired Gossamer securities between June 16, 2025, and February 20, 2026, and you wish to serve as lead plaintiff in this lawsuit, you are encouraged to submit your information to DiCello Levitt LLP via the form on this page. 

You can also contact DiCello Levitt attorneys Brian O’Mara and Hani Farah by calling (888) 287-9005 or at investors@dicellolevitt.com. 

The deadline to apply to the Court to serve as a lead plaintiff in the Gossamer class action lawsuit is June 1, 2026.