---
schema_version: "secwatch.filing_event.v1"
accession: "0001104659-21-117017"
form_type: "8-K"
ticker: "PTGX"
cik: "0001377121"
company_name: "Protagonist Therapeutics, Inc"
filed_at: "2021-09-17T23:59:59+00:00"
generated_at: "2026-06-29T02:54:45.608251+00:00"
event_type: "regulatory"
sentiment: "negative"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# FDA places clinical hold on Protagonist's rusfertide program after tumor finding in mouse study

## Summary
- FDA clinical hold on all rusfertide studies after rasH2 mouse model showed benign/malignant subcutaneous skin tumors.
- Four cancer cases observed across rusfertide trials assessed as unrelated; company providing additional safety data to FDA.
- Dosing paused in all ongoing trials; investigators contacted to notify patients.
- Rusfertide is a Phase 2 hepcidin mimetic for polycythemia vera and hereditary hemochromatosis.

## SEC filing metadata
- accession: 0001104659-21-117017
- form_type: 8-K
- ticker: PTGX
- cik: 0001377121
- company_name: Protagonist Therapeutics, Inc
- filed_at: 2021-09-17T23:59:59+00:00
- event_type: regulatory
- sentiment: negative
- 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/1377121/000110465921117017/0001104659-21-117017-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1377121/000110465921117017/tm2127921d1_8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001104659-21-117017
- JSON: https://secwatch.observer/filing/0001104659-21-117017.json
- Plain text: https://secwatch.observer/filing/0001104659-21-117017.txt

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