A legal fight escalated between GSK (via Tesaro) and AnaptysBio over licensing terms tied to the cancer immunotherapy Jemperli. Tesaro filed suit alleging Anaptys breached the 2014 collaboration agreement; Anaptys responded by filing a Verified Complaint seeking a court declaration that Tesaro materially breached the contract and that Anaptys retains rights and remedies. The dispute centers on testing and development choices, alleged breaches and future royalty streams tied to Jemperli sales, which have contributed substantial revenue and milestone prospects. Both companies have pursued parallel actions including an amended repurchase plan and public statements; the litigation could determine licensing rights, milestone payments and Anaptys’ plans to monetize royalties.