Cabometyx® (cabozantinib (L)-malate)
Case Name: Exelixis, Inc. v. MSN Labs. Private Ltd., No. 2025-1236, 2026 WL 2560739 (Fed. Cir. Aug. 31, 2026) (Circuit Judges Moore, Stoll, and Moore presiding; Opinion by Stoll, J.) (Appeal from D. Del., Andrews, J.)
Drug Product and Patent(s)-in-Suit: Cabometyx® (cabozantinib (L)-malate); U.S. Patent Nos. 11,091,439 (“the ’439 patent”), 11,091,440 (“the ’440 patent”), and 11,098,015 (“the ’015 patent”), and 11,298,349 (“the ’349 patent”)
Nature of the Case and Issue(s) Presented: Exelixis holds the NDA for Cabometyx, which is indicated for treating kidney, liver, and differentiated thyroid cancers. All of the patents, except for the ’349 patent, share a specification and claim, respectively, crystalline cabozantinib (L)-malate salts, pharmaceutical formulations containing those salts, and methods of treating cancer with the salts. Although the specification specifically describes two crystalline polymorphs of cabozantinib (L)-malate, N-1 and N-2, the asserted claims encompass crystalline cabozantinib (L)-malate more broadly. MSN filed an ANDA seeking approval for generic cabozantinib (L)-malate tablets using a different crystalline polymorph, form S. MSN conceded infringement and argued that those patents were invalid for lack of adequate written description under 35 U.S.C. § 112(a) because the specification did not demonstrate possession of the broader genus of crystalline cabozantinib (L)-malate salts. Following a bench trial, the district court rejected MSN’s written-description challenge and entered judgment that the patents-in-suit were infringed and not invalid. The Federal Circuit affirmed.
Why Exelixis Prevailed: The Federal Circuit affirmed the district court’s finding of adequate written description. Applying Ariad, the court explained that a claimed genus may be adequately described either by disclosure of a representative number of species or by disclosure of structural features common to the genus that permit a skilled artisan to visualize or recognize its members. The Federal Circuit found no clear error in the district court’s determination that the specification satisfied the latter route. Specifically, the disclosure identified the chemical name and formula of cabozantinib (L)-malate and the common structural characteristic that the salt is crystalline. Those characteristics adequately identified the claimed genus because the claims themselves required nothing more than cabozantinib (L)-malate salt having a crystalline structure. The specification also disclosed processes for making the invention. The court analogized the case to GlaxoSmithKline LLC v. Banner Pharmacaps, Inc., emphasizing that the claims contained no functional or performance limitation requiring the claimed compounds to perform a particular function or produce a particular result.
The Federal Circuit rejected MSN’s argument that the specification’s disclosure of only the N-1 and N-2 polymorphs was insufficient because other polymorphs could possess different densities, melting points, solubilities, hygroscopicity, vapor pressures, and stability characteristics. Those properties were not claimed, and the district court did not rely on them to define the genus. Rather, the relevant common structural features were the chemical name and formula of cabozantinib (L)-malate and its crystalline structure. The court also distinguished cases such as AbbVie, noting that the maximum potential size of the pure-polymorph genus was only fourteen forms and therefore did not raise the concerns associated with genus claims potentially encompassing vast numbers of materially different species. Because structural features common to the genus adequately described the claimed invention, Exelixis was not separately required to establish that the specification disclosed a representative number of species.
The appeal also involved claim 3 of the ’349 patent, which claims an oral cabozantinib (L)-malate composition “essentially free” of a particular genotoxic impurity, defined by the specification as 200 ppm or less. The district court had found that MSN’s product did not infringe that claim but also rejected MSN’s argument that the claim was inherently disclosed by the prior art and therefore invalid. Exelixis initially cross-appealed the noninfringement ruling but voluntarily dismissed that appeal, making the judgment of noninfringement final. MSN subsequently conceded that its validity appeal was moot and sought vacatur of the district court’s no-invalidity ruling. The Federal Circuit agreed, rejecting Exelixis’s contention that possible collateral consequences in separate litigation involving a continuation patent preserved a live controversy. Because Exelixis’s unilateral dismissal of its cross-appeal prevented MSN from obtaining appellate review of the validity ruling, the Federal Circuit dismissed MSN’s appeal concerning the ’349 patent as moot and vacated the district court’s judgment that claim 3 was not invalid.
