Federal Circuit Upholds Crystalline Salt Genus Claims

October 2026

In Exelixis, Inc. v. MSN Laboratories Private Ltd., No. 2025-1236 (Fed. Cir. Aug. 31, 2026), the Federal Circuit affirmed that claims to a genus of crystalline salt forms of a drug compound were adequately supported under the written description requirement, even though the specification specifically described only two polymorphs.

Exelixis owns a number of patents covering its cancer drug Cabometyx®, whose active ingredient is cabozantinib (L)-malate (the “Malate Salt Patents”). The Malate Salt Patents claim the genus of crystalline cabozantinib (L)-malate salts. However, the specification only specifically describes two polymorphs, N-1 and N-2. When MSN filed an abbreviated new drug application (ANDA) for generic cabozantinib (L)-malate tablets using a different polymorph, form S, Exelixis sued for infringement. The district court found that MSN infringed the Malate Salt Patents and rejected MSN’s written description defense, holding that the specification’s disclosure of the genus’s common structural features, e.g., chemical name, formula, and crystalline nature, was sufficient. MSN appealed the validity rulings.

The Federal Circuit affirmed the written description holding. It held that the district court did not clearly err in concluding that the chemical name, formula, and requirement of a crystalline structure were structural features sufficient to define the claimed genus and distinguish it from other materials. The court rejected MSN’s argument that the differing physical properties of the N-1 and N-2 polymorphs, e.g., density, melting point, solubility, and vapor pressure, precluded support for a genus encompassing other polymorphs, reasoning that those properties were not claimed. Unlike cases in which genus claims have been held invalid, the claims here were no broader than what the specification described: crystalline cabozantinib (L)-malate salt.

Author: John Klaczany

Edited by Craig Drachtman

For more articles like this, click the link below:

https://www.lernerdavid.com/news-successes/case-clips