GSK (Tesaro) and AnaptysBio have moved into dual litigation in Delaware over a decade‑old licensing agreement for the cancer drug Jemperli. GSK sued first seeking termination of the deal and a permanent license; AnaptysBio countered with a Verified Complaint alleging Tesaro materially breached the Collaboration and Exclusive License Agreement and tortiously interfered with it. The dispute centers on testing and partnership rights tied to Jemperli’s commercial performance and milestone payments. Jemperli’s recent sales trajectory — cited in filings — makes the royalty and milestone stakes material to AnaptysBio’s financial planning, including a planned royalty business spin‑off.