First Delaware Anti-SLAPP Ruling: Prelitigation Demand Letters Not Injury-Producing Conduct in Anticipatory Breach Claims

WILMINGTON (LN) — Delaware's Court of Chancery on Thursday dismissed an anticipatory-breach claim brought by a GlaxoSmithKline subsidiary against cancer-drug partner AnaptysBio, ruling that the GSK unit failed to show AnaptysBio's October 7 demand letter conveyed repudiation in the "unequivocal, positive, and unconditional" terms Delaware law requires — while also issuing the state's first ruling on the nexus requirement under its newly enacted Uniform Public Expression Protection Act.

The dispute centers on a 2014 Collaboration and Exclusive License Agreement governing dostarlimab, a cancer therapy marketed under the brand name Jemperli. Tesaro, Inc. and its subsidiary Tesaro Development, Ltd. — both wholly owned by GlaxoSmithKline — sued AnaptysBio after the biotech sent a letter on October 7, 2025 accusing Tesaro of at least three material breaches of the agreement, including participating in clinical trials involving a dostarlimab competitor, failing to seek the drug's "optimum commercial return," and concealing development activities from AnaptysBio.

Tesaro claimed the letter itself evidenced repudiation and filed a claim for anticipatory breach. AnaptysBio moved to dismiss on two grounds: failure to state a claim under Rule 12(b)(6), and separately, under UPEPA — Delaware's anti-SLAPP statute, adopted just weeks before the dispute erupted on September 15, 2025.

The court granted the motion on the pleading ground and denied it on the anti-SLAPP ground, producing a split ruling that resolved both questions as matters of first impression under the new statute.

On the contract claim, the court found the October 7 letter fell short because AnaptysBio conditioned any termination on the parties' failure to resolve their disagreement through the Collaboration Agreement's own 30-day dispute resolution process. The letter did not convey an unconditional intent to never perform. Rather, the notice of termination was expressly conditioned on the contract dispute process, which was designed to eliminate the need for termination.

Tesaro also pointed to AnaptysBio's November 3 letter, in which the biotech stated that nothing in Tesaro's response would "dissuade AnaptysBio from exercising its right to dostarlimab's reversion." The court rejected that argument, finding that a threat to exercise contractual rights in the event of breach is not repudiation — it is an affirmation of the agreement. The court further noted that even if the letters had supported a repudiation claim, the Collaboration Agreement's 60-day cure period ran at least until December 6, 2025, and AnaptysBio's continued performance and the parties' joint stipulation to preserve the status quo effectively retracted any repudiation before that window closed.

The more consequential portion of the opinion addressed UPEPA. AnaptysBio argued that its prelitigation communications constituted protected activity under Section 6002(b)(2) of the statute and that Tesaro's anticipatory-breach claim arose from those communications. The court assumed without deciding that the letters qualified as protected activity, but held that AnaptysBio failed to establish the required nexus — that the protected activity was itself the injury-producing conduct, not merely evidence of it.

According to the opinion, a claim may be struck only if the speech or petitioning activity itself is the wrong complained of, and not just evidence of liability or a step leading to some different act for which liability is asserted. The wrong in an anticipatory-breach claim, the court held, is the act of repudiation — not the letter through which it was communicated. No matter how the decision to repudiate was conveyed, the injury in a claim for anticipatory breach is the act of repudiation, not the way it was communicated.

Tesaro sought fees and costs for defeating the anti-SLAPP motion, but the court declined to award them, finding the motion was neither frivolous nor filed solely to delay. Because the UPEPA nexus question had never been addressed by a Delaware court, the court concluded each side must bear its own fees and costs.

The parties filed mirror-image suits on November 20, 2025, the day their standstill agreement expired, and have stipulated to preserve the status quo — meaning AnaptysBio will not send a termination notice or attempt to exercise reversion rights, and Tesaro will not seek to reduce royalty payments or convert its licenses to perpetual ones — through final judgment.