---
schema_version: "secwatch.filing_event.v1"
accession: "0001370053-25-000103"
form_type: "8-K"
ticker: "ANAB"
cik: "0001370053"
company_name: "ANAPTYSBIO, INC"
filed_at: "2025-11-26T23:59:59+00:00"
generated_at: "2026-05-16T16:26:33.352117+00:00"
event_type: "litigation"
sentiment: "negative"
materiality_score: 0.8
calibrated_materiality_score: 0.8
confidence: "high"
source: SEC EDGAR
---

# AnaptysBio sues Tesaro and GSK for breach of collaboration agreement on dostarlimab

## Summary
- AnaptysBio filed suit in Delaware Chancery Court on Nov 20, 2025, alleging material breach of the Collaboration Agreement by Tesaro and GSK.
- Complaint seeks declaration that rights to dostarlimab revert to AnaptysBio within 60 days of notice of material breach.
- Allegations include Tesaro/GSK conducting clinical trials with competing PD-1 (Keytruda) instead of optimizing dostarlimab's commercial return, and failing to disclose trials.
- This follows a 2020 settlement where Tesaro/GSK paid $60M and doubled royalties; AnaptysBio claims violations continued post-settlement.
- Tesaro and GSK filed a counterclaim on Nov 26, 2025, claiming AnaptysBio breached the agreement.

## SEC filing metadata
- accession: 0001370053-25-000103
- form_type: 8-K
- ticker: ANAB
- cik: 0001370053
- company_name: ANAPTYSBIO, INC
- filed_at: 2025-11-26T23:59:59+00:00
- event_type: litigation
- sentiment: negative
- materiality_score: 0.8
- calibrated_materiality_score: 0.8
- confidence: high
- sec_items: 7.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1370053/000137005325000103/0001370053-25-000103-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1370053/000137005325000103/anab-20251126.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001370053-25-000103
- JSON: https://secwatch.observer/filing/0001370053-25-000103.json
- Plain text: https://secwatch.observer/filing/0001370053-25-000103.txt

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