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

ANAPTYSBIO, INC

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.

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