GSK’s Tesaro unit has dealt a blow to its legal battle with Jemperli developer AnaptysBio, with a Delaware court dismissing GSK’s breach of contract claims ahead of a trial scheduled for July.
The latest information comes from the Delaware Court of Chancery, which rejected Tesaro’s claims that AnaptysBio breached the Jemperli license agreement between the two companies, meaning that GSK’s request for a reduction in royalties to AnaptysBio was also dismissed.
Dan Faga, CEO of AnaptisBio, said in a statement that the decision “confirms what we have argued from the beginning: Tesaro’s anticipatory breach claims are without merit and this judgment is an important validation of our efforts to protect Gemperi’s contractual rights to the royalty stream on behalf of our shareholders.”
The legal dispute dates back to November, when GSK’s Tesaro took Gemperi’s partners to court for “recent actions” that breached the contract, giving the GSK subsidiary the right to terminate the contract, obtain a “perpetual and irrevocable” license for its own drug, and reduce outstanding royalty and milestone payments by 50%, the company said at the time.
GSK said in its own statement on Monday that the new judgment “does not address the merits of the main contractual dispute between the parties and does not affect Tesaro’s remaining claims against Anaptis Bio seeking a declaratory judgment.”
GSK said Tesaro filed the lawsuit after AnaptisBio claimed that Tesaro had not met certain requirements of the agreement and had expressed an interest in regaining the license.
Upon hearing AnaptysBio’s story, Tesaro filed a lawsuit “without notice” after AnaptysBio attempted to have “good faith discussions,” prompting AnaptysBio to file its own complaint in Delaware state court.
AnaptisBio alleges that Tesaro violated multiple terms of the companies’ 2014 cooperation agreement, including by participating in development efforts for Gemperi’s rival PD-1 drugs, including Merck & Co.’s Keytruda.
The trial is scheduled for July 14-17 of this year.
If Tesaro is found to have violated any of the terms of the contract at trial, Gemperi’s license will only be returned to AnaptisBio, the biotech company said.
GSK, which acquired oncology drug maker Tesaro in 2019, is already in a battle with AnaptysBio over another Tesaro drug, Zejula. Although the companies ultimately settled for cash and royalties, Anaptis Bio used similar allegations regarding a planned study involving Keytruda “without Anaptis’ consent,” the company said.
GSK called its endometrial cancer drug Genperi the “cornerstone” of its immuno-oncology research and development program and reported sales of the drug in 2025 of £861 million ($1.16 billion). Losing the Gemperi license to Anaptis Bio would be a major loss for the company’s oncology ambitions, given that it remains committed to expanding Gemperi’s indications, including the possibility of subcutaneous administration of the drug.
