Exelixis, Inc. v. MSN Laboratories Private Ltd., Appeal No. 2025-1236 (Fed. Cir. Aug. 31, 2026)

In our Case of the Week, the Federal Circuit upheld the validity of several patents covering Exelixis’ blockbuster cancer drug Cabometyx, delaying availability of generic versions of the drug.  The Court found three of Exelixis’ patents supported by adequate written description, and while MSN Labs. also appealed a “no invalidity” finding on a fourth patent, the Federal Circuit dismissed that appeal as moot after Exelixis abandoned its appeal of the lower court’s finding that it was not infringed.

Exelixis sued MSN Labs in 2019 over an Abbreviated New Drug Application implicating Exelis patents on crystalline cabozantinib (L)-malate salts (the “Malate Salt Patents,” U.S. Patent Nos. 11,091,439, 11,091,440, and 11,098,015) and a separate patent (No. 11,298,349) directed to a cabozantinib composition essentially free of a genotoxic impurity.  These cabozantinib “salts” are ingredients central to the production of Cabometyx.  MSN conceded infringement of the Malate Salt Patents but argued they were invalid for lack of written description under 35 U.S.C. § 112(a), and separately contested infringement and validity of the ’349 patent.  After a bench trial, the district court found the Malate Salt Patents infringed and not invalid—and the ’349 patent not infringed but also not invalid—leading MSN to appeal all of the validity rulings.  The Federal Circuit affirmed the written description holdings for the ’439, ’440, and ’015 patents, but dismissed as moot and vacated the district court’s no-invalidity judgment on claim 3 of the ’349 patent.

Under the two-part test from Ariad Pharmaceuticals v. Eli Lilly, 598 F.3d 1336 (Fed. Cir. 2010), which explained that a sufficient written description for disclosure of a claimed genus requires disclosure of either a representative number of species within the genus, or structural features common to the genus members such that a skilled artisan can “visualize or recognize” those members, with a precise definition by structure, formula, chemical name, or other distinguishing properties.  Here, the Federal Circuit held there was no clear error in finding that disclosure of the chemical name and formula of cabozantinib (L)-malate salt, plus the fact that its structure is crystalline, adequately identified the structural features shared by genus members, and that the Malate Salt Patents’ claims were no broader than this description since they simply required a crystalline salt.

The court’s reasoning leaned heavily on analogy to GlaxoSmithKline v. Banner Pharmacaps (“GSK”), 744 F.3d 725 (Fed. Cir. 2014), where description of a drug complex by structure alone was found sufficient to allow one of skill in the art to “visualize or recognize the identify of the members of the genus.”  Id. at 730.  Like in GSK, the Malate Salt Patents’ claims recited no performance property that the compounds must achieve, so the case raised no issue of insufficient structural or process description to support a functional limitation.  The court rejected MSN’s argument that differences in density, melting point, solubility, and other properties among the disclosed compounds undermined written description for the full genus because MSN had failed to explain why those unclaimed property differences were relevant, since the district court never relied on them to identify the genus’ structural features (it had relied on the chemical name, formula, and crystalline structure).  The court also noted, without dispute from MSN, that the maximum possible size of any compound genus was fourteen forms, meaning the case did not raise the concerns generally associated with genus claims covering vast, unpredictable chemical spaces.  The court further distinguished prior cases where challenged specifications affirmatively disclosed only a narrower embodiment of what was ultimately claimed, because here, the claimed subject matter (a crystalline cabozantinib (L)-malate salt) was no broader than what the challenged specification described.  The court also clarified that the district court had not applied a relaxed standard for structural claims, but had merely recognized, consistent with Ariad, that functional claim language can make it more challenging to supply adequate written description.

On the ’349 patent, MSN abandoned its merits appeal after Exelixis voluntarily dismissed its own cross-appeal on infringement, rendering the noninfringement judgment final and eliminating any live controversy over invalidity.  The court explained that a validity challenge does not automatically become moot upon a noninfringement finding, but because Exelixis’ own litigation choice had eliminated any redressable injury and because Exelixis’ argument that the ruling could have speculative collateral consequences in a separate suit involving a related patent was too hypothetical, Exelixis lacked standing and so dismissed MSN’s appeal as to claim 3 of the ’349 patent as moot and vacated the district court’s judgment of no invalidity under the Munsingwear/Bancorp vacatur doctrine.

The full opinion can be found here.

By Jason Evans

Netlist, Inc. v. Micron Tech., Inc. et al., Appeal No. 2024-1707 (Fed. Cir. Sept. 2, 2026)

In an appeal from a final decision of obviousness by the US patent office in an inter parties review, the Federal Circuit considered a number of arguments by appellant Netlist, including various arguments arising under the Administrative Procedure Act (“APA”).  Under one of these APA-related arguments, Netlist argued that the Board’s conclusion of obviousness relied upon a combination of prior art references not advanced in the challenger’s petition.  However, the Court concluded that any potential error by the Board was harmless, because the Board alternatively found that a prior art reference from the petition, alone, establishes the obviousness of the claims.  The Court was unpersuaded by a number of other arguments by Appellant, including other APA related arguments, and affirmed the Board’s conclusion of obviousness.

The opinion can be found here.

By Michael Cofield

Constellation Designs, LLC v. LG Electronics, Inc., Appeal No. 2024-1822 (Fed. Cir. Aug. 31, 2026)

On a motion for panel rehearing, the Federal Circuit reissued a 32-page opinion that it had previously issued in April, modifying one footnote, apparently to address the basis for the motion.  We covered this case in our Fresh From the Bench write-up on May 4, 2026, which can be found here.  As noted in that discussion, the Federal Circuit reversed the district court with respect to a number of patent claims, finding them to be invalid.  LG argued that the damages award should be reversed as a result.  In a footnote in its original opinion, the Federal Circuit had noted that the argument was waived because LG failed to raise it before oral argument.  The Court also wrote that, in any event, Constellation’s damages expert “testified that the value of Constellation’s asserted patents was tied to the technology rather than any asserted patent or claim.”  Apparently LG sought rehearing on this latter statement in the footnote, because the Court reissued the opinion striking that portion of the footnote, relying instead exclusively on the fact that the argument was waived for failing to raise it in the opening brief.

The reissued opinion can be found here.

By Nika Aldrich

This article summarizes aspects of the law and does not constitute legal advice. For legal advice with regard to your situation, you should contact an attorney.