AnaptysBio Moves to Toss GSK/Tesaro Repudiation Claim Over Jemperli Royalties

AnaptysBio filed a partial motion to dismiss on Dec. 30, 2025, challenging an anticipatory‑breach claim brought by TESARO, Inc., the oncology unit now owned by GlaxoSmithKline plc, over royalties from sales of the cancer drug Jemperli (dostarlimab). The filings were unsealed and made public on Jan. 8, 2026, setting the stage for a procedural hearing expected by early March and a trial scheduled for July 14–17, 2026.

The dispute traces to a 2014 Collaboration and Exclusive License Agreement under which AnaptysBio is entitled to receive royalties linked to Jemperli through at least the expiration of composition‑of‑matter patent coverage, cited as 2035 in the United States and 2036 in Europe. Tesaro initiated the Delaware Chancery Court action on Nov. 20, 2025, alleging that Anaptys repudiated the agreement and seeking a judicial declaration that Tesaro had not breached the deal. Multiple sources state Tesaro filed the suit "without notice to Anaptys" while the parties were engaged in discussions.

Anaptys responded by filing its own complaint, asserting that Tesaro materially breached the Collaboration Agreement and alleging that GSK tortiously interfered with the contractual relationship. In its motion to dismiss Tesaro’s anticipatory‑breach count, Anaptys argues that it never repudiated the agreement and that its efforts to vindicate contractual rights cannot constitute anticipatory breach. The company frames that defense "as a matter of law" and has also invoked Delaware’s anti‑SLAPP statute, alleging Tesaro’s suit is a strategic attempt to chill or punish Anaptys’ good‑faith assertion of legal rights.

The litigation centers on more than contractual formalities. Royalties on blockbuster oncology drugs fund early‑stage research and development at smaller companies and can influence investor confidence in nascent biotech firms. For patients and health systems, the dispute carries implications for drug pricing and supply arrangements, especially where long patent protections, here stretching into the mid 2030s, anchor royalty calculations and licensing strategies. A protracted fight could affect forecasting, reimbursement negotiations, and the pace at which competitors or biosimilars enter the market after patent expiry.

Market reaction was immediate. On Jan. 8, 2026, one market snapshot showed AnaptysBio shares at $43.80, down 3.12 percent on the day and roughly 9.65 percent over five trading days. Analysts remain divided; in the prior six months 11 analysts issued price targets with a median of $56.00, underscoring differing views on the company’s near‑term prospects and the value of any royalty stream.

Legal observers say the early procedural rulings will shape the contours of the July trial. If the court grants Anaptys’ motion to dismiss Tesaro’s anticipatory‑breach claim, the remaining allegations, Anaptys’ breach claim against Tesaro and its tortious interference claim against GSK, will determine whether Anaptys is entitled to royalties and potential damages. For stakeholders beyond the courtroom, patients, payers, and other biotech partners, the case will be a bellwether for how disputes over licensing, corporate consolidation, and litigation posture affect access to essential cancer therapies and the financial stability of small innovators.