GSK’s Tesaro unit has suffered a legal setback in its dispute with Jemperli developer AnaptysBio, as a Delaware court dismissed GSK’s contract breach claim. The ruling, issued ahead of a scheduled July trial, also tossed GSK’s request to slash the royalties owed to AnaptysBio by 50% for the oncology blockbuster Jemperli.
The legal conflict originated last November when Tesaro sued AnaptysBio, claiming “conduct” that entitled the GSK subsidiary to cancel the agreement and obtain a “perpetual and irrevocable” license at significantly reduced royalty rates. Conversely, AnaptysBio asserts that Tesaro breached multiple provisions of their 2014 collaboration, including participating in development activities with rival PD-1 drugs such as Merck’s Keytruda.
GSK noted that the latest ruling does not address the merits of the principal contractual dispute and has no impact on remaining claims. However, AnaptysBio maintains that if Tesaro is found to have breached even one provision at trial, the Jemperli license will return solely to the biotech firm. With 2025 sales reaching $1.16 billion, Jemperli is considered the “foundation” of GSK’s immuno-oncology program. Losing the license would represent a major loss for the company’s oncology ambitions.