---
schema_version: "secwatch.filing_event.v1"
accession: "0001728117-26-000004"
form_type: "8-K"
ticker: "GOSS"
cik: "0001728117"
company_name: "Gossamer Bio, Inc."
filed_at: "2026-02-23T23:59:59+00:00"
generated_at: "2026-05-16T01:12:22.093454+00:00"
event_type: "other_material"
sentiment: "neutral"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# Gossamer Bio Phase 3 PROSERA trial misses primary endpoint, seralutinib shows signals in high-risk PAH

## Summary
- Primary 6MWD endpoint missed: +13.3m placebo-adjusted (p=0.0320 vs prespecified α=0.025).
- Four key secondary endpoints favored seralutinib; NT-proBNP reduced 120.4 ng/L (p=0.0002).
- In intermediate/high-risk (REVEAL Lite 2 ≥6, n=234), 6MWD gain +20.0m (p=0.0207).
- Gossamer to meet with FDA to discuss path forward; pauses SERANATA study enrollment.
- Seralutinib well tolerated; cough (37%) and transaminase elevations >3x ULN (13%) reported.

## SEC filing metadata
- accession: 0001728117-26-000004
- form_type: 8-K
- ticker: GOSS
- cik: 0001728117
- company_name: Gossamer Bio, Inc.
- filed_at: 2026-02-23T23:59:59+00:00
- event_type: other_material
- sentiment: neutral
- materiality_score: 0.85
- calibrated_materiality_score: 0.85
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1728117/000172811726000004/0001728117-26-000004-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1728117/000172811726000004/goss-20260223.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001728117-26-000004
- JSON: https://secwatch.observer/filing/0001728117-26-000004.json
- Plain text: https://secwatch.observer/filing/0001728117-26-000004.txt

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