Tesaro, Inc. v. Anaptysbio, Inc.

── Tesaro, Inc. v. Anaptysbio, Inc. ── Court: Court of Chancery of Delaware Date: April 24, 2026 Category: General IN THE COURT OF CHANCERY OF THE STATE OF DELAWARE TESARO, INC., and ) TESARO DEVELOPMENT, ) LTD., ) ) Plaintiffs, ) ) v. ) C.A. No. 2025-1357-KSJM ) ANAPTYSBIO, INC., ) Defendant. ) MEMORANDUM OPINION Date Submitted: March 4, 2026 Date Decided: April 24, 2026 David E. Ross, Eric D. Selden, ROSS ARONSTAM & MORITZ LLP, Wilmington, DE; Stephen J. Kastenberg, William B. Igoe, Elizabeth P. Weissert, Paul K. Ort, BALLARD SPAHR LLP, Philadelphia, PA; Paul Spagnoletti, Brett M. McMahon, Ryan W. Cooke, Marie Killmond, DAVIS POLK & WARDWELL LLP, New York, NY; Counsel for Plaintiffs Tesaro, Inc. and TESARO Development, Ltd. Ryan D. Stottmann, Brian P. Egan, Alec F. Hoeschel, Andrew Schoen, MORRIS, NICHOLS, ARSHT & TUNNELL LLP, Wilmington, DE; Robert Counihan, Vanessa Park-Thompson, Nicholas Klenow, FENWICK & WEST LLP, New York, NY; Counsel for Defendant AnaptysBio, Inc. McCORMICK, C.  The parties dispute their rights and obligations under a collaboration agreement. The collaboration agreement contains a dispute resolution provision. On October 7, 2025, the defendant sent notice to the plaintiffs teeing up the dispute as required by the dispute resolution provision. The parties then agreed to a standstill period to negotiate a resolution. Negotiations failed. On the day that the standstill period expired, the parties filed mirror-image claims under the collaboration agreement. The plaintiffs in this action also alleged that the defendant’s October 7 letter evidenced repudiation and asserted a claim of anticipatory breach. The defendant has moved to dismiss the claim of anticipatory breach on two grounds. First, the defendant argues that the complaint fails to state a claim. Second, the defendant argues that the claim of anticipatory breach should be dismissed under Delaware’s recently amended anti-SLAPP statute. This decision grants the defendant’s motion to dismiss on the first ground—the plaintiffs failed to allege that the defendant conveyed repudiation with unequivocal, positive, and unconditional words or conduct, as required under Delaware law. This decision rejects the defendant’s argument under the anti-SLAPP statute. To have a claim struck under the anti-SLAPP statute, a movant must establish a nexus between the cause of action and the protected activity. Here, the defendant has not established the relevant nexus because the claim of anticipatory breach arises from the act of repudiation, not the October 7 letter allegedly evidencing the repudiation. I. FACTUAL BACKGROUND The facts are drawn from the Complaint,1 the documents it incorporates by reference, and facts subject to judicial notice.2 AnaptysBio, Inc. owns proprietary technology to discover antibodies used to treat diseases. Tesaro, Inc. (together with its wholly owned subsidiary Tesaro Development, Ltd., “Tesaro”) develops and commercializes transformational medicines that improve, sustain, and extend the lives of cancer patients. Tesaro is a wholly owned subsidiary of GlaxoSmithKline LLC (together with its non-Tesaro affiliates, “GSK”). On March 10, 2014, AnaptysBio and Tesaro entered into a Collaboration and Exclusive License Agreement (the “Collaboration Agreement”).3 The parties made at least three amendments to the Collaboration Agreement.4 The Collaboration Agreement governs the parties’ rights and obligations to a cancer therapy called dostarlimab, which is marketed under the brand name Jemperli. In July 2025, Tesaro and GSK told AnaptysBio that they had designed and approved a Phase 3 clinical trial that would allow p