GSK's Tesaro Sues AnaptysBio Over Jemperli License Dispute

(RTTNews) - GSK plc (GSK), a biopharmaceutical company's subsidiary Tesaro, Inc. (TSRO), on Friday announced that it has filed litigation in the Delaware Chancery Court against AnaptysBio, Inc. (ANAB), alleging a material breach of their license agreement covering the oncology drug Jemperli or dostarlimab.

Tesaro says that AnaptysBio's recent actions violate the 2014 agreement, giving it the right to terminate the existing license, secure a perpetual and irrevocable licence to dostarlimab, and reduce related royalties and milestone payments by 50 percent.

The lawsuit follows AnaptysBio's claims that Tesaro failed to meet certain contractual obligations and that it intends to revoke Tesaro's license.

GSK and Tesaro say the allegations from AnaptysBio are entirely without merit.

GSK and Tesaro continue to advance a broad clinical program evaluating dostarlimab in additional cancers, including rectal, colon, and head and neck.

Jemperli is approved in more than 35 countries for certain endometrial cancers, with strong growth driven by recent label expansions in the U.S. and EU.

GSK closed trading 0.50% lesser at $46.11 on the New York Stock Exchange.

AnaptysBio closed the regular trading session on November 20, 2025, at $37.66, up $0.65 or 1.76%. Later, in overnight trading, the share price decreased to $36.43, gaining $1.23 or 3.27%, as of 2.25 AM EST.