LONDON, April 25, 2026, 19:03 BST
GSK plc’s Tesaro unit lost an early Delaware court ruling in its licensing fight with AnaptysBio over Jemperli, after the Court of Chancery dismissed Tesaro’s claim that Anaptys had anticipatorily breached their cancer-drug collaboration agreement. The decision, issued Friday, keeps the broader dispute alive rather than ending it.
The timing is awkward for GSK. The London-listed drugmaker reports first-quarter results on Wednesday, April 29, at 0700 BST, with investors looking for proof that oncology and other specialty medicines can keep carrying growth under Chief Executive Luke Miels.
GSK has told investors to expect 2026 turnover growth of 3% to 5% at constant exchange rates, a measure that strips out currency moves, and has kept a 2031 sales outlook above £40 billion. Miels said in February the year would bring a “strong focus on commercial launches and accelerating R&D.” GSK
Company-compiled analyst consensus dated April 16 puts GSK’s first-quarter turnover at £7.58 billion, with specialty medicines expected at £3.23 billion, ahead of vaccines at £2.03 billion and general medicines at £2.32 billion. That is where Jemperli matters.
The case centers on Jemperli, known generically as dostarlimab, an immunotherapy used in endometrial cancer, a cancer of the lining of the uterus. The U.S. Food and Drug Administration expanded Jemperli’s approval in 2024 for use with chemotherapy, followed by single-agent treatment, in adults with primary advanced or recurrent endometrial cancer.
Anaptys said the ruling preserves current contracted royalty rates and rejects Tesaro’s request for a royalty reduction. Dan Faga, Anaptys’ president and chief executive, called the decision “an important validation” of the company’s effort to protect its Jemperli royalty stream. AnaptysBio, Inc.
Court records show the parties failed to settle after a standstill period and then filed mirror claims. In plain terms, Tesaro argued Anaptys had clearly walked away from the deal before its obligations were due; the court said Tesaro had not pleaded the clear, unconditional repudiation required under Delaware law.
GSK’s prior public position has been blunt. When Tesaro filed the case in November, GSK said Anaptys’ allegations were “entirely without merit” and argued that the alleged breach entitled Tesaro to terminate the current license, secure a perpetual license to dostarlimab and cut royalties and milestones due to AnaptysBio by 50%. GSK
The dollars are meaningful. Anaptys says Jemperli generated $1.128 billion, or £861 million, in 2025 sales and that GSK has guided to more than £2 billion in peak monotherapy sales for the drug.
There is also competitive heat. Anaptys has alleged Tesaro violated exclusivity terms by taking part in trials with rival PD-1 drugs, including Merck & Co’s Keytruda; PD-1 drugs are cancer immunotherapies that work on an immune checkpoint pathway. Reuters reported earlier that Anaptys also accused GSK of favoring other oncology programs over Jemperli.
But Friday’s order is narrow. It does not decide whether Tesaro breached the agreement, nor whether Anaptys can win reversion of Jemperli rights at the July 14-17 trial; a ruling that upsets GSK’s economics or control over the drug would be far more serious than this pleading-stage loss.
With London trade shut for the weekend, GSK shares last closed at 2,020 pence on Friday, down 2.7%, according to Reuters market data. The stock is now heading into results week with a legal overhang that is small next to GSK’s whole business, but awkwardly placed near one of its key growth stories.
