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On 20 November 2025, GSK subsidiary TESARO, Inc. initiated litigation against AnaptysBio, Inc. in the Delaware Chancery Court. TESARO contends AnaptysBio materially breached their March 2014 license agreement concerning Jemperli (dostarlimab), asserting an entitlement to terminate the agreement, obtain a perpetual and irrevocable license, and reduce royalties and milestone payments due by 50%.
| Date | 21 Nov 2025 |
| Time | 07:00:13 |
| Category | Miscellaneous |
| ID | 4514I |
Issued: 20 November 2025, London UK
TESARO, a GSK subsidiary, initiates litigation against AnaptysBio, Inc.
GSK plc (LSE/NYSE: GSK) subsidiary, TESARO, Inc., confirms it has initiated litigation against AnaptysBio, Inc. in the Delaware Chancery Court. This action contends that recent conduct by AnaptysBio is in material breach of the existing license agreement with TESARO regarding the oncology treatment Jemperli (dostarlimab). The breach entitles TESARO to terminate the current license agreement, obtain a perpetual and irrevocable license to dostarlimab, and to reduce the royalties and milestone payments due by TESARO to AnaptysBio by 50%.
TESARO has initiated this litigation following allegations made by AnaptysBio that TESARO has not fulfilled certain requirements of the license agreement entered in March 2014 and that AnaptysBio intends to revoke TESARO's licence for dostarlimab. GSK and TESARO are firmly of the view that these allegations are entirely without merit.
Jemperli is currently approved in over 35 countries for use in certain endometrial cancers, the most common gynaecologic cancer in the United States. GSK and TESARO have reported significant growth for Jemperli driven by label expansions in endometrial cancer, including in the US and EU. A robust and ambitious clinical trial programme to evaluate the potential use of dostarlimab in additional cancers, including rectal, colon and head and neck, is ongoing.
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GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Such factors include, but are not limited to, those described in the "Risk Factors" section in GSK's Annual Report on Form 20-F for 2024, and GSK's Q3 Results for 2025.
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