GSK’s Tesaro unit took a blow in its legal feud with Jemperli developer AnaptysBio, with a Delaware court dismissing GSK’s contract breach claim ahead of a planned trial in July.
The update comes from the Delaware Chancery Court, which rejected Tesaro’s claims that AnaptysBio breached the Jemperli license agreement between the two, meaning that GSK’s request to reduce the royalties owed to AnaptysBio was also tossed.
In a statement, AnaptysBio CEO Dan Faga said the decision “affirms what we have maintained from the beginning: Tesaro’s anticipatory breach claim was baseless, and this ruling is an important validation of our efforts to protect our contractual rights to the Jemperli royalty stream for our shareholders.”
The legal conflict stems back to November, when GSK’s Tesaro brought its Jemperli partner to court over “recent conduct” that it said constituted a contract breach and entitled the GSK subsidiary to cancel the agreement, obtain its own “perpetual and irrevocable” license to the drug and slash its owed royalties and milestone payments by 50%, the company said at the time.
On Monday, GSK pointed out that the new ruling “does not address the merits of the principal contractual dispute between the parties and has no impact on Tesaro’s remaining claim against AnaptysBio for declaratory judgment,” the company said in its own statement.
According to GSK, Tesaro initiated the litigation after AnaptysBio alleged that Tesaro fell short of meeting certain requirements in the contract and voiced an interest in snatching back the license.
To hear AnaptysBio tell it, Tesaro brought its suit “without notice” following AnaptysBio’s attempts to engage in “good faith discussions,” prompting AnaptysBio to file its own complaint in the Delaware court.
AnaptysBio asserts that Tesaro breached multiple provisions in the 2014 collaboration agreement between the two, including by participating in development activities with rival PD-1 drugs to Jemperli, such as Merck’s Keytruda.
The trial is scheduled for July 14-17 of this year.
If Tesaro is found to have breached even one of the contract provisions at trial, Jemperli’s license will return solely to AnaptysBio, the biotech said.
GSK, which bought oncology drugmaker Tesaro in 2019, has already gone to bat with AnaptysBio regarding another Tesaro med, Zejula. Although the two eventually settled with a cash payment and a royalty, AnaptysBio had leveraged similar allegations concerning a planned study that included Keytruda “without the consent of Anaptys,” it said.
GSK calls endometrial cancer drug Jemperli the “foundation” of its immuno-oncology R&D program and reported 861 million pounds sterling ($1.16 billion) in 2025 sales of the drug. Losing its Jemperli license to AnaptysBio would mark a major loss for the company’s oncology ambitions, considering that it is still working on expanding Jemperli’s reach, including with a potential subcutaneous version of the drug.