Background
Exelixis holds the New Drug Application for Cabometyx, a cancer drug containing cabozantinib (L)-malate. After MSN sought approval to market generic tablets using its own crystalline form of that compound, Exelixis sued for infringement of four patents. Three patents—the ’439, ’440, and ’015 patents—claim crystalline cabozantinib (L)-malate salts, formulations containing them, and methods of treating cancer with them. MSN conceded infringement of the asserted claims but argued that they lacked adequate written description under 35 U.S.C. § 112(a).
The fourth patent, the ’349 patent, claims an oral pharmaceutical composition that is essentially free of a genotoxic impurity. Following a bench trial, the District of Delaware held the asserted claims of the first three patents infringed and not invalid. It also held claim 3 of the ’349 patent not infringed and not invalid. Exelixis initially cross-appealed the noninfringement ruling but dismissed that cross-appeal before briefing, making the noninfringement judgment final.
The Court’s Holding
The Federal Circuit affirmed the ruling that the asserted claims of the ’439, ’440, and ’015 patents satisfy the written-description requirement. The specification disclosed structural features common to the claimed genus: the chemical name and formula of cabozantinib (L)-malate and the requirement that the salt be crystalline. Those disclosures allowed a skilled artisan to recognize the genus’s members, and the specification also described processes for making the invention. The court found no clear error in the district court’s factual findings.
The court rejected MSN’s argument that differences in density, melting point, solubility, and other properties among polymorphs defeated written-description support. Those properties were not claimed, and MSN did not show why they undermined the specification’s identification of the genus by shared structural features. As to claim 3 of the ’349 patent, the court held that MSN’s appeal had become moot after Exelixis abandoned its cross-appeal of noninfringement. Because Exelixis’s unilateral action prevented appellate review of the adverse validity ruling, the court dismissed that portion of MSN’s appeal and vacated the district court’s judgment that claim 3 was nonobvious.
Key Takeaways
- A patent can adequately describe a chemical genus by disclosing structural features common to its members; it need not necessarily disclose a representative number of species as well.
- Unclaimed differences in physical properties among crystalline polymorphs do not establish inadequate written description when the specification identifies the claimed genus through shared chemical and structural characteristics.
- When an appellee’s unilateral action moots an appeal and prevents review of an adverse judgment, vacatur may be appropriate to clear the way for future litigation.
Why It Matters
The decision preserves Exelixis’s asserted crystalline-salt, formulation, and treatment claims against MSN’s generic Cabometyx product. It also confirms that structurally defined pharmaceutical genus claims may satisfy § 112(a) even when disclosed polymorphs have differing physical properties, particularly where no performance limitation is claimed and the genus is not potentially vast.
The vacatur ruling limits the effect of the district court’s obviousness analysis concerning the ’349 patent. Although noninfringement remains final, the vacated nonobviousness judgment cannot stand as an unreviewed determination that could impede future litigation.