Shares of Gossamer Bio fell more than 75% on February 23, 2026, after the company announced that its Phase 3 PROSERA trial evaluating seralutinib in pulmonary arterial hypertension failed to meet its primary endpoint. The disclosure follows an August 5, 2025 company release in which management expressed confidence in the program’s scientific foundation and indicated that commercial planning was underway ahead of the anticipated topline results. Block & Leviton is investigating.
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