Gossamer Bio's PAH drug fails pivotal trial, sending stock into freefall

Gossamer Bio's experimental drug seralutinib has failed a key clinical trial in pulmonary arterial hypertension (PAH). The setback follows a promising start, including a rare FDA Breakthrough Therapy designation in 2022. Now, the company's future hinges on an upcoming meeting with regulators.

Seralutinib, also known as PROSERA, showed early potential in Phase 2 trials. Data from that stage revealed improvements in pulmonary vascular resistance and patients' walking ability. These results earned it a Breakthrough Therapy designation—a status shared by only a handful of approved PAH treatments like macitentan and selexipag.

The Phase 3 trial, however, missed its primary goal in late 2025. Instead of improving walk distance, the drug failed to deliver the expected benefits. This failure triggered a sharp decline in Gossamer Bio's stock, which now trades at around $0.42. Since January, shares have dropped by roughly 86%, pushing the company's market value down to $99 million. Analysts have reacted with caution. Cantor Fitzgerald downgraded the stock from 'Overweight' to 'Neutral' after the trial results. Opinions remain split, with price targets ranging from $0.30 to $15.00, averaging $5.43. Some recommend selling, while others still see potential. Gossamer Bio has scheduled a 'Type C' meeting with the FDA for June. The company aims to discuss possible paths forward for seralutinib. Concrete outcomes from this meeting are expected by July, just after the next quarterly results on May 12. The failed trial now threatens the entire development program for the drug.

The failed Phase 3 trial leaves Gossamer Bio in a difficult position. The company's next steps depend on the FDA's feedback in June. Until then, investors and analysts will watch closely for any signs of recovery or further decline.