GSK, AnaptysBio Sue Each Other Over Cancer Drug License — Update

By Elena Vardon

Drugmaker GSK and U.S. biotechnology company AnaptysBio started litigation against each other, with each saying the other party breached a licensing agreement for cancer treatment Jemperli.

Tesaro, a subsidiary of Britain's GSK, said it took legal action against Anaptys in the Delaware Chancery Court, citing recent conduct by the company that Tesaro said breaches a licensing agreement for Jemperli.

Separately, Anaptys said it filed a complaint in the same Delaware court requesting a declaration that Tesaro breached the collaboration and license agreement, that GSK interfered with the deal, and that Anaptys is entitled to all rights and remedies under the agreement.

The litigation centers on Jemperli, a drug used to treat some forms of endometrial cancer. Anaptys originally discovered the drug and licensed it to Tesaro as part of a broader collaboration agreement in 2014. GSK reported sales of 600 million pounds ($784.4 million) for Jemperli in the first nine months of 2025, up 89% on year.

The GSK subsidiary said its move came in response to allegations by Anaptys that it hadn't fulfilled some of the requirements of the agreement and Anaptys intended to revoke the deal. GSK and Tesaro view these allegations as without merit, it added.

Tesaro said it is entitled to terminate the current license agreement, get a perpetual and irrevocable license to Jemperli, and cut the royalties and milestone payments to Anaptys by half.

Meanwhile, Anaptys said Tesaro violated its exclusivity obligations by participating in clinical trials with drugs that compete with Jemperli and failed to secure an optimum commercial return for the drug.

Anaptys said it approached Tesaro to engage in talks in good faith to try to solve the claims before Tesaro launched the lawsuit without notice. Anaptys said Tesaro's claims are without merit, in its view, and that it intends to pursue all appropriate legal remedies.

A trial is expected to take place in July, Anaptys said. Anaptys said it will continue to be owed milestone and royalty payments included in the agreement during the proceedings.

Write to Elena Vardon at elena.vardon@wsj.com

(END) Dow Jones Newswires

November 21, 2025 05:55 ET (10:55 GMT)