Tags: layoffs, cardiology, phase-3, merck

Gossamer Bio Cuts 48% of Staff After Phase 3 Seralutinib Failure — Merck's Winrevair Holds Its Position in PAH

By FieldPulse Editorial · March 21, 2026

Gossamer Bio eliminated 77 positions — nearly half its workforce — after its Phase 3 PROSERA trial of seralutinib in pulmonary arterial hypertension missed its primary endpoint. The failure removes a key near-term competitive threat to Merck's Winrevair in the rapidly evolving PAH market.

Gossamer Bio announced on March 17, 2026 that it would eliminate approximately 77 employees — close to 48% of its total workforce — after the Phase 3 PROSERA trial of seralutinib in pulmonary arterial hypertension (PAH) failed to meet its primary endpoint.

Seralutinib was one of the most closely watched PAH pipeline agents, designed as a direct competitor to Merck's Winrevair (sotatercept), which launched in 2024 as the first new PAH mechanism in over a decade.

Sotatercept works by blocking activin signaling to reduce pulmonary vascular remodeling — a fundamentally different approach from the vasodilator-based drugs that dominated PAH therapy for years.

Winrevair has been a commercial success and is rapidly becoming the anchor of combination PAH regimens at leading academic centers.

Seralutinib, also an activin pathway modulator, was expected to offer similar mechanism-based benefits with potentially improved tolerability.

The PROSERA trial showed a placebo-adjusted 13.3-meter improvement on the six-minute walk test — the primary endpoint — but the result was not statistically significant.

Gossamer Bio will now conserve cash, explore strategic options, and retain its small approved COPD product.

The company held approximately $100 million in cash at last reporting, providing limited runway.

What it means for reps: Merck's Winrevair field force just lost its most credible near-term competitive threat.

Reps selling sotatercept in PAH can now consolidate their position without an imminent competitor entering the activin pathway space.

Reps at established PAH players — United Therapeutics (Tyvaso, Orenitram), J&J (Tracleer, Opsumit), and Janssen — should note that the PAH competitive landscape has one fewer pipeline entrant.