LONDON, April 25, 2026, 19:03 BST
Tesaro, the GSK plc subsidiary, took a hit Friday when the Delaware Court of Chancery tossed out its claim that AnaptysBio had anticipatorily breached their Jemperli cancer-drug partnership. The court’s move leaves the door open for the larger licensing dispute to continue.
It’s a tough moment for GSK. The drugmaker, listed in London, is set to release its first-quarter numbers on Wednesday, April 29, at 0700 BST. Investors want to see evidence that the company’s push into oncology and specialty drugs under Chief Executive Luke Miels is still driving growth.
GSK is sticking with its forecast for turnover growth of 3% to 5% in 2026, measured at constant exchange rates to exclude currency swings, and it continues to project sales topping £40 billion in 2031. Back in February, Miels pointed to a “strong focus on commercial launches and accelerating R&D” for the year. GSK
Analysts polled by GSK as of April 16 project first-quarter turnover of £7.58 billion. Specialty medicines are seen leading at £3.23 billion, trailed by general medicines at £2.32 billion, and vaccines at £2.03 billion. Jemperli sits squarely in that specialty medicines number.
The dispute focuses on Jemperli—dostarlimab’s brand name—an immunotherapy prescribed for endometrial cancer, which affects the uterus lining. In 2024, the U.S. Food and Drug Administration broadened Jemperli’s label: now it can be given alongside chemo, then continued as a solo agent, for adults facing primary advanced or recurrent cases.
Anaptys announced that the court upheld its existing contracted royalty rates, turning down Tesaro’s bid to lower them. Dan Faga, who serves as president and CEO, described the outcome as “an important validation” of Anaptys’ push to safeguard its Jemperli royalty revenue. AnaptysBio, Inc.
According to court filings, both sides filed matching claims after talks broke down post-standstill. Tesaro’s argument? Anaptys supposedly abandoned the agreement before any duties kicked in. But the court found Tesaro fell short—no clear, outright repudiation as Delaware law demands.
GSK hasn’t minced words in public. After Tesaro brought the lawsuit in November, the company dismissed Anaptys’ claims as “entirely without merit.” GSK maintains that, if there was a breach, Tesaro would have grounds to end the current license, lock in a perpetual license for dostarlimab, and slash both royalties and milestone payments to AnaptysBio by half. GSK
The numbers tell the story. Anaptys reports Jemperli sales hit $1.128 billion, or £861 million, in 2025. GSK’s expectations? They’re aiming for over £2 billion in peak monotherapy sales from the drug.
The competitive pressure is unmistakable. Anaptys claims Tesaro broke exclusivity agreements by getting involved with trials for competing PD-1 drugs, such as Merck & Co’s Keytruda. These PD-1 therapies target the immune checkpoint pathway in cancer. On top of that, Reuters previously noted Anaptys has accused GSK of putting its support behind other oncology projects instead of Jemperli.
Friday’s order, though, sticks to a narrow lane. It leaves open the question of whether Tesaro actually broke the contract, and doesn’t decide if Anaptys can claw back Jemperli rights at the trial set for July 14-17. A ruling that undermines GSK’s hold on the drug—or its economics—would carry much bigger implications than this setback in the pleading stage.
London markets are closed for the weekend, so GSK finished Friday at 2,020 pence, slipping 2.7%, Reuters market data show. As results week approaches, the company is carrying a legal overhang—minor in the context of GSK’s scale, but sitting uncomfortably close to one of its main growth narratives.
