---
schema_version: "secwatch.filing_event.v1"
accession: "0001728117-25-000040"
form_type: "8-K"
ticker: "GOSS"
cik: "0001728117"
company_name: "Gossamer Bio, Inc."
filed_at: "2025-06-16T23:59:59+00:00"
generated_at: "2026-05-19T06:37:27.042017+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# Gossamer Bio completes enrollment in Phase 3 PROSERA study for seralutinib in PAH (n=390)

## Summary
- Global registrational Phase 3 PROSERA study fully enrolled; topline results expected February 2026.
- Enrolled 390 patients vs 86 in Phase 2; mean 6MWD 374 m (vs 408 m), NT-proBNP 987 ng/L (vs 628).
- 74% of patients are Functional Class III vs 42% in Phase 2; enrichment criteria applied to target responders.
- Study is double-blind, placebo-controlled, primary endpoint change in 6MWD at week 24.
- Seralutinib developed with Chiesi Group; positive milestone for first-in-class PAH treatment.

## SEC filing metadata
- accession: 0001728117-25-000040
- form_type: 8-K
- ticker: GOSS
- cik: 0001728117
- company_name: Gossamer Bio, Inc.
- filed_at: 2025-06-16T23:59:59+00:00
- event_type: other_material
- sentiment: positive
- materiality_score: 0.85
- calibrated_materiality_score: 0.85
- confidence: high
- sec_items: 7.01, 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1728117/000172811725000040/0001728117-25-000040-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1728117/000172811725000040/goss-20250616.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001728117-25-000040
- JSON: https://secwatch.observer/filing/0001728117-25-000040.json
- Plain text: https://secwatch.observer/filing/0001728117-25-000040.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.