Gossamer Bio Faces Class Actions After Phase 3 PROSERA Misses Primary Endpoint

Overview

• Gossamer announced on February 23, 2026 that its Phase 3 PROSERA study of seralutinib failed to meet the primary six‑minute‑walk‑distance endpoint at Week 24.
• Company executives said the result was driven by an outsized placebo response and regional heterogeneity concentrated at Latin American sites where patients were described as more heavily treated and lower risk.
• The topline failure sent Gossamer shares down roughly 80% in one day and the company later disclosed it had traded below Nasdaq’s $1 minimum bid price starting February 24, 2026 and reported that condition on April 9, 2026.
• Multiple law firms have filed securities complaints alleging Gossamer withheld material information about trial design and site monitoring, and firms are actively soliciting investors to seek lead‑plaintiff status before the June 1, 2026 deadline.
• All allegations are unproven and key next steps include courts deciding lead‑plaintiff motions, the progress of the litigation, and whether Nasdaq takes further action on the company’s listing status, outcomes that will shape investor recoveries and Gossamer’s future plans.