Gossamer Bio, Inc. (GOSS)

Gossamer Bio is a clinical-stage biopharmaceutical company focused on developing and commercializing seralutinib, an investigational inhaled small-molecule inhibitor of PDGFR (alpha and beta isoforms), CSF1R and c-KIT, for pulmonary hypertension (PH), including pulmonary arterial hypertension (PAH) and PH associated with interstitial lung disease (PH-ILD). PAH is a rare, progressive and often fatal disease driven by abnormal cell proliferation and remodeling of the small blood vessels of the lung, with an estimated US patient population of about 50,000 and over 70,000 in the EU. Seralutinib is designed to address the underlying remodeling and to improve on the efficacy seen with oral imatinib while avoiding its systemic safety and tolerability problems, using a convenient inhaled delivery system.

In February 2026, the company reported topline results from the 390-patient Phase 3 PROSERA trial, which showed a placebo-adjusted 13.3-meter improvement in six-minute walk distance at Week 24 but missed the prespecified alpha threshold. Consistent with the earlier Phase 2 TORREY study, results were stronger in intermediate- and high-risk patients and in a connective tissue disease-associated PAH subgroup. Near-term priorities include completing PROSERA analyses, seeking FDA feedback (including a Type C meeting) on a regulatory path, advancing NDA-readiness activities, continuing open-label extension studies, and strengthening the capital structure, including evaluating alternatives for its outstanding convertible notes.

Enrollment in the Phase 3 SERANATA study in PH-ILD is paused. Seralutinib was in-licensed from Pulmokine and has orphan drug designation for PAH from the FDA, the European Commission and Japan's PMDA. Under a May 2024 collaboration agreement with Chiesi, the company leads global development in PAH and PH-ILD and shares US commercialization of those indications equally with Chiesi, which leads development in any additional indications and holds exclusive commercialization rights outside the United States.

The company also holds an option agreement with Respira Therapeutics for RT234, an on-demand PAH and PH-ILD candidate that it is advancing in a capital-efficient manner.