On August 31, 2026, the Federal Circuit issued a precedential opinion in Exelixis, Inc. v. MSN Laboratories Private Ltd., No. 2025-1236 (Stoll, J., joined by Moore, C.J., and District Judge Moore, sitting by designation). The appeal is from a District of Delaware bench trial (Judge Richard G. Andrews) in Nos. 1:22-cv-00228-RGA and 1:22-cv-00945-RGA, reported at 2024 WL 4491176 (D. Del. Oct. 15, 2024).
The ANDA fight
Exelixis holds the NDA for Cabometyx, a tablet of cabozantinib (L)-malate used in kidney, liver, and differentiated thyroid cancer. MSN filed ANDA No. 213878 for a generic, using form S of cabozantinib (L)-malate. The asserted claims of U.S. Patents 11,091,439, 11,091,440, and 11,098,015 (the Malate Salt Patents) were conceded infringed; MSN challenged written description. Claim 3 of U.S. Patent 11,298,349 was found not infringed and not invalid. On appeal, MSN challenged written description of claim 4 of the '439 patent, claim 3 of the '440 patent, and claim 2 of the '015 patent, and originally also the no-inherency finding on claim 3 of the '349 patent.
Written description
A genus can be described by disclosing a representative number of species, or structural features common to the members so a skilled artisan can visualize or recognize them. Ariad Pharmaceuticals, Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1350 (Fed. Cir. 2010). The court found no clear error in treating the chemical name and formula of cabozantinib (L)-malate salt, plus the requirement that the salt is crystalline, as those structural features. The claims are no broader than that disclosure. The specification also discloses processes used to make the invention, which is not independently dispositive. The analogy to GlaxoSmithKline LLC v. Banner Pharmacaps, Inc., 744 F.3d 725 (Fed. Cir. 2014), held: the claims recite no performance property that would require more structural support. Differences in density, melting point, and similar unclaimed properties of the N-1 and N-2 polymorphs did not show clear error, and did not bring the case within AbbVie Deutschland GmbH & Co. v. Janssen Biotech, Inc., 759 F.3d 1285 (Fed. Cir. 2014). The district court found a maximum potential size of fourteen pure polymorph forms. The Federal Circuit did not need to reach the representative-species path.
The '349 vacatur
Exelixis dropped its cross-appeal of the noninfringement finding on claim 3 of the '349 patent. That left MSN appealing a validity judgment on a claim it had already been held not to infringe. After the court flagged standing, MSN moved to dismiss that portion as moot and to vacate. The court granted the motion: Exelixis's unilateral decision to drop the cross-appeal frustrated merits review of the no-inherency finding, so the nonobviousness judgment on claim 3 is vacated under the Munsingwear/Bancorp line. A continuation of the '349 patent, U.S. Patent 12,128,039, is already in later litigation; that is background, not a holding in this appeal.
What it means in practice
For crystalline-salt genus claims without functional limitations, naming the salt and requiring a crystalline structure can be enough written description when the district court's fact findings hold up. It is not a free pass for large, functionally defined genus claims. Separately, dropping a cross-appeal of noninfringement can cost you the validity judgment you won below, via vacatur rather than affirmance.
What to watch next
Whether MSN seeks further review of the salt patents, and how the later '039 litigation (noted in the opinion) treats the now-vacated claim 3 judgment.