GSK’s Tesaro subsidiary and AnaptysBio have filed cross‑complaints in Delaware court over a decade‑old license for the cancer immunotherapy Jemperli. GSK asked the court to terminate the agreement, seek a permanent license and cut royalties, alleging AnaptysBio breached contract terms. AnaptysBio countersued, claiming Tesaro’s conduct violated licensing provisions and jeopardized milestone and royalty payments tied to Jemperli sales. The litigation centers on testing and commercial rights tied to Jemperli, which recorded roughly £600 million in sales through the first nine months of 2025. Both companies flagged the dispute’s materiality to future revenue streams: AnaptysBio has a strategic plan to spin off a royalty business by 2026, and preserving Jemperli income is central to those plans. The case will affect partnership negotiations and diligence in future PD‑1/PD‑L1 collaborations.