---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-25-125881"
form_type: "8-K"
ticker: "PRTA"
cik: "0001559053"
company_name: "PROTHENA CORP PUBLIC LTD CO"
filed_at: "2025-05-23T23:59:59+00:00"
generated_at: "2026-05-20T14:15:47.947725+00:00"
event_type: "other_material"
sentiment: "negative"
materiality_score: 0.9
calibrated_materiality_score: 0.9
confidence: "high"
source: SEC EDGAR
---

# Prothena's Phase 3 AFFIRM-AL trial for birtamimab fails; development halted; workforce reduction planned

## Summary
- Phase 3 AFFIRM-AL did not meet primary endpoint of all-cause mortality (HR=0.915, p=0.7680); secondary endpoints also missed.
- Birtamimab development discontinued; open-label extension stopped.
- Company to substantially reduce workforce and operating expenses; further update expected in June 2025.
- Birtamimab was generally safe and well-tolerated, consistent with prior safety profile.
- Upcoming data: PRX012 Phase 1 ASCENT (Alzheimer's) in August; partner updates from Roche, Novo Nordisk, BMS in 2025-2026.

## SEC filing metadata
- accession: 0001193125-25-125881
- form_type: 8-K
- ticker: PRTA
- cik: 0001559053
- company_name: PROTHENA CORP PUBLIC LTD CO
- filed_at: 2025-05-23T23:59:59+00:00
- event_type: other_material
- sentiment: negative
- materiality_score: 0.9
- calibrated_materiality_score: 0.9
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1559053/000119312525125881/0001193125-25-125881-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1559053/000119312525125881/d891971d8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-25-125881
- JSON: https://secwatch.observer/filing/0001193125-25-125881.json
- Plain text: https://secwatch.observer/filing/0001193125-25-125881.txt

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