---
schema_version: "secwatch.filing_event.v1"
accession: "0001370053-25-000096"
form_type: "8-K"
ticker: "ANAB"
cik: "0001370053"
company_name: "ANAPTYSBIO, INC"
filed_at: "2025-11-21T23:59:59+00:00"
generated_at: "2026-05-16T17:35:06.996381+00:00"
event_type: "other_material"
sentiment: "negative"
materiality_score: 0.8
calibrated_materiality_score: 0.8
confidence: "high"
source: SEC EDGAR
---

# AnaptysBio sues Tesaro and GSK for breach of Jemperli collaboration; countersuit filed

## Summary
- AnaptysBio alleges Tesaro breached exclusivity by conducting trials with competing PD-1 antagonists (e.g., Keytruda) and failing to maximize Jemperli return.
- Tesaro countersued AnaptysBio on Nov 20, 2025, seeking injunctive relief; AnaptysBio calls claims meritless and will seek dismissal.
- Parties agreed to expedited Delaware Chancery Court schedule; trial anticipated July 2026.
- Milestone and royalty payments under Collaboration Agreement remain due during litigation.

## SEC filing metadata
- accession: 0001370053-25-000096
- form_type: 8-K
- ticker: ANAB
- cik: 0001370053
- company_name: ANAPTYSBIO, INC
- filed_at: 2025-11-21T23:59:59+00:00
- event_type: other_material
- sentiment: negative
- materiality_score: 0.8
- calibrated_materiality_score: 0.8
- confidence: high
- sec_items: 8.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1370053/000137005325000096/0001370053-25-000096-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1370053/000137005325000096/anab-20251120.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001370053-25-000096
- JSON: https://secwatch.observer/filing/0001370053-25-000096.json
- Plain text: https://secwatch.observer/filing/0001370053-25-000096.txt

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