Seagen Inc. v. Daiichi Sankyo Co., Ltd.

Authored by: Jeremy J. Gustrowsky

A recent decision from the Federal Circuit has brought clarity to the requirements for written description and enablement in patent law, with significant implications for pharmaceutical and biotech patents. The case centered on U.S. Patent No. 10,808,039, owned by Seagen Inc., which claimed a specific type of antibody-drug conjugate (ADC) used in cancer treatment. Seagen had sued Daiichi Sankyo Company, Ltd. and AstraZeneca over their cancer drug Enhertu®, alleging infringement of the ‘039 patent.

At the heart of the dispute was whether Seagen’s patent was valid. The patent claimed a linker structure in ADCs made only from glycine and phenylalanine amino acids—a subgenus of 81 possible tetrapeptides. However, the original 2004 patent application, from which Seagen claimed priority, disclosed a much broader range of possible peptide linkers—over 47 million combinations—but did not specifically mention or highlight the all-glycine/phenylalanine tetrapeptide group. This omission became critical when Daiichi challenged the patent’s validity, arguing that the original application did not adequately describe or enable the claimed invention.

The Federal Circuit agreed with Daiichi, finding that the original application’s broad disclosure did not provide “reasonably specific supporting disclosure” for the narrow group of peptides claimed in the ‘039 patent. The court emphasized that simply listing a vast number of possibilities does not show that the inventors actually possessed the specific invention at the time of filing. Notably, the court cited testimony from Seagen’s own inventors, who admitted they had not contemplated the specific linker structure until after Daiichi’s Enhertu was publicly disclosed.

The court also found that the patent failed the enablement requirement. Because the patent claimed any drug moiety that could be intracellularly cleaved from the antibody, but did not provide a common quality or clear guidance for achieving this function across the full scope of the claim, a skilled artisan would have to engage in extensive trial-and-error experimentation. The court likened this to the Supreme Court’s recent decision in Amgen v. Sanofi, where a similar lack of guidance for a broad genus of antibodies led to invalidation.

As a result, the court reversed the district court’s decision, invalidated the ‘039 patent, and vacated the jury’s finding of willful infringement and damages award. This case serves as a reminder that broad claims in biotech patents must be supported by specific disclosures and clear instructions for making and using the full scope of the invention.