In November 2025, the U.S. Court of Appeals for the Federal Circuit delivered a significant ruling in Duke University v. Sandoz Inc., reversing a $39 million jury verdict and invalidating a patent claim for lack of adequate written description. This decision underscores the court’s stringent approach to the written description requirement, particularly concerning chemical genus claims.
The case centered on U.S. Patent No. 9,579,270 (the ‘270 patent), co-owned by Duke University and Allergan Sales, LLC. The patent pertains to methods for treating hair loss using prostaglandin F (PGF) analogs. Allergan markets Latisse®, a topical solution for eyelash growth containing bimatoprost, a PGF analog. Sandoz Inc. developed a generic version of Latisse®, leading to the infringement lawsuit.
At trial, Sandoz contended that claim 30 of the ‘270 patent was invalid due to an insufficient written description. The jury, however, found in favor of Duke and Allergan, awarding $39 million in damages. Sandoz appealed, challenging the adequacy of the patent’s written description.
The Federal Circuit’s analysis focused on whether the ‘270 patent’s specification demonstrated that the inventors possessed the full scope of the claimed invention at the time of filing. The court noted that while the specification broadly disclosed billions of PGF analogs, claim 30 was limited to a subgenus of approximately 1,620 to 4,230 compounds. Crucially, the specification did not provide a single example of a compound within this subgenus nor did it delineate common structural features that would enable a skilled artisan to identify the claimed compounds.
The court emphasized the necessity of “blaze marks”—clear guidance within the specification that directs a skilled artisan to the claimed subgenus. In this instance, the ‘270 patent’s specification offered numerous options for various positions on the PGF analogs without prioritizing or highlighting the specific combinations that define the claimed subgenus. This lack of direction left the skilled artisan to navigate a vast array of possibilities without clear guidance.
Furthermore, the court observed that the specification’s preferred embodiments did not align with the claimed subgenus, effectively leading away from the claimed invention rather than toward it. This misalignment further undermined the adequacy of the written description.
Consequently, the Federal Circuit concluded that no reasonable jury could find that the ‘270 patent satisfied the written description requirement. The court reversed the district court’s judgment, invalidating claim 30 for lack of adequate written description.
This ruling reinforces the Federal Circuit’s stringent standards for written descriptions in patent law, particularly for chemical genus claims. Patent applicants must ensure that their specifications either provide a representative number of species within the claimed genus or clearly identify common structural features with sufficient “blaze marks” to guide a skilled artisan to the claimed subgenus. Failure to do so may result in claims being invalidated for lack of adequate written description.
The decision serves as a critical reminder for patent practitioners to meticulously document and describe inventions, especially when dealing with broad genus claims, to meet the rigorous requirements set forth by the Federal Circuit.