Gossamer Bio announced its Phase 3 PROSERA trial failed to meet the primary endpoint for seralutinib in pulmonary arterial hypertension (PAH); the observed six‑minute walk distance improvement did not reach statistical significance. The trial recorded cough and elevated liver enzymes among adverse events, raising tolerability questions. Despite the miss, Gossamer said it will continue regulatory engagement and pursue FDA approval pathways, citing supportive secondary data and safety signals that may inform next steps. The outcome complicates commercial prospects in PAH and underscores the uncertainty in translating early‑stage efficacy into late‑stage success, prompting reevaluation of timelines and resource allocation.