Gossamer Bio disclosed that its Phase 3 PROSERA trial of seralutinib in pulmonary arterial hypertension missed the primary endpoint, producing a non‑statistically significant 13‑meter six‑minute walk distance benefit versus placebo. The clinical setback was accompanied by safety signals including cough and liver enzyme elevations. Investors reacted violently: the company’s shares plunged roughly 77% after the release. Management said it will still pursue regulatory options despite the miss, while analysts flagged the result as an important datapoint for inhaled or locally delivered PAH approaches and for commercial prospects of seralutinib.