AnaptysBio initiates litigation against GSK subsidiary Tesaro

AnaptysBio (ANAB) announced it has filed a Verified Complaint in Delaware Chancery Court, requesting a court declaration that Tesaro has materially breached the parties’ collaboration and exclusive license agreement and that GSK (GSK) has tortiously interfered with the collaboration agreement. Anaptys has requested that the court declare that Anaptys is entitled to all rights and remedies under the collaboration agreement. The company said, “The Complaint contends that Tesaro breached, and GSK induced Tesaro to breach, multiple material Collaboration Agreement terms. Under these terms, Tesaro agreed that it would not conduct or participate in research, development, manufacturing or commercialization of any PD-1 antagonist other than those licensed by Anaptys to Tesaro. The Collaboration Agreement also provides that Tesaro will “use Commercially Reasonable Efforts to . . . obtain the optimum commercial return for (Jemperli) in all major markets throughout the world.” Despite these obligations, the Complaint contends that Tesaro violated its exclusivity obligations by participating in past, ongoing, and upcoming governed clinical trials with PD-1 antagonists that compete with Jemperli, including Keytruda, and failed to use Commercially Reasonable Efforts to obtain the “optimum commercial return” for Jemperli by, among other things, participating in a course of conduct with GSK to favor GSK’s antibody-drug conjugate product candidates, including by pairing those ADCs with PD-1 antagonists that directly compete with Jemperli. In 2020, Anaptys similarly filed a complaint against GSK regarding breaches of its obligations under the Collaboration Agreement. Those breaches at the time related to GSK’s planned clinical trial of Zejula, another of GSK’s oncology programs, in combination with Keytruda, without the consent of Anaptys. This planned trial violated Tesaro’s exclusivity obligations. This complaint resulted in a settlement that included a cash payment, a royalty on Zejula and a substantial increase in royalties on sales of Jemperli due to Anaptys. While Anaptys had approached Tesaro to engage in good faith discussions to potentially resolve these claims, on Nov. 20, 2025, Tesaro, without notice, initiated a lawsuit against Anaptys. Tesaro’s complaint includes requests for injunctive relief, claiming that Anaptys has breached the Collaboration Agreement. Tesaro’s claim for breach is predicated on an allegation that Anaptys has improperly alleged that Tesaro had breached the Collaboration Agreement. Tesaro seeks to improperly restrain Anaptys from exercising its legal rights under the Collaboration Agreement in violation of Delaware’s anti-SLAPP statute and other legal protections. Anaptys contends that Tesaro’s claims are entirely without merit and intends to pursue all appropriate legal remedies against Tesaro, including dismissal of such claims at the earliest opportunity and the potential for additional litigation. The parties have agreed to request an expedited schedule with the Delaware Chancery Court, with trial anticipated in July 2026. Milestone and royalty payment obligations to Anaptys pursuant to the Collaboration Agreement continue to be due during the proceedings.”