Gossamer Bio PROSERA Study Failure Lawsuits

Gossamer Bio is facing multiple securities class action lawsuits following the announcement on February 23, 2026, that its Phase 3 PROSERA study for seralutinib, a treatment for pulmonary arterial hypertension, failed to meet its primary endpoint. The company's stock price plummeted by 80% on this news. The lawsuits, filed by firms including Pomerantz LLP, Bronstein, Gewirtz & Grossman, LLC, The Schall Law Firm, Faruqi & Faruqi, Hagens Berman, The Gross Law Firm, and The Law Offices of Frank R. Cruz, allege that Gossamer Bio and its officers made false and misleading statements and failed to disclose material adverse facts regarding the study's design, particularly concerning the placebo response at Latin American testing sites. These sites reportedly enrolled a heavily treated, lower-risk population, leading to an unexpectedly strong placebo performance that diluted the overall treatment effect. Additionally, Gossamer Bio has not met the minimum share bid price required for continued listing on the Nasdaq-100.