AnaptysBio Inc. (NASDAQ:ANAB) has pushed back against claims that it breached its long-standing licensing deal tied to the cancer drug Jemperli, asking a Delaware court to dismiss what it calls an improper lawsuit brought by Tesaro while there are ongoing royalty disputes.
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The clinical-stage biotech argues it has acted within its contractual rights and is seeking judicial clarity as litigation with Tesaro and its parent company, GSK Plc (NYSE:GSK), moves toward trial.
The dispute centers on a Collaboration and Exclusive License Agreement that entitles Anaptys to royalties on sales of Jemperli, an immunotherapy used to treat certain solid tumors.
The underlying agreement dates back to March 2014, when Anaptys entered into the collaboration with Tesaro, then an independent oncology-focused biopharmaceutical company, later acquired by GSK.
Under the deal, Tesaro develops Jemperli both as a monotherapy and in combination regimens. Anaptys is eligible for tiered royalties ranging from 8% to 25% of net sales, with royalty obligations extending through U.S. patent expiration in 2035 and EU protection through 2036.
According to court filings, Anaptys previously approached Tesaro to engage in good-faith discussions aimed at resolving alleged breaches of that agreement by Tesaro and GSK.
While those discussions were ongoing, Tesaro filed suit in November 2025, without prior notice, asserting that Anaptys had repudiated the contract and seeking a declaration that Tesaro had not breached the agreement.
Anaptys responded by filing its own complaint in Delaware Chancery Court, asking the court to declare that Tesaro materially breached the contract and that GSK tortiously interfered with the agreement.
In December 2025, Anaptys escalated the matter by filing a partial motion to dismiss Tesaro's anticipatory breach of contract claim.
The motion, which was unsealed in January 2026, argued that Anaptys never repudiated the agreement and merely sought to enforce its contractual rights. The company contended that, under Delaware law, asserting those rights cannot constitute repudiation.
Anaptys also maintained that Delaware's anti-SLAPP statute applied to the case, characterizing Tesaro's lawsuit as a strategic attempt to deter legitimate legal claims. Anti-SLAPP laws are designed to prevent litigation aimed at chilling good-faith efforts to assert legal rights.
Tesaro and GSK countered that Anaptys' motion to dismiss should pause discovery.
Anaptys disputed that position, particularly as the parties prepare for a trial currently scheduled for July 14–17. The court was expected to hear Anaptys' motion by early March, in line with the timing requirements of Delaware's anti-SLAPP law.
In November 2025, AnaptysBio discontinued the Phase 2 trial of rosnilimab for moderate-to-severe ulcerative colitis as it did not meet the primary endpoint of the mean change from baseline in the modified Mayo Score (severity of ulcerative colitis, mMS) or the key secondary endpoints of clinical response and clinical remission at week 12.
ANAB Price Action: AnaptysBio stock is up 4.02% at $45.56 at publication on Friday.
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