Seagen v Daiichi Sankyo (Fed. Cir., December 2, 2025) 2023-2424

This episode presents an opinion from the United States Court of Appeals for the Federal Circuit, resolving a patent dispute between Seagen Inc. and Daiichi Sankyo Company, Ltd. concerning an antibody-drug conjugate (ADC) cancer treatment. Seagen had previously secured a jury verdict in the Eastern District of Texas finding that Daiichi's drug, Enhertu®, willfully infringed the ’039 patent and awarded Seagen over $41 million in damages. However, the Federal Circuit reversed the district court’s denial of judgment as a matter of law (JMOL), finding the ’039 patent to be invalid. The court ruled that the patent failed to meet the written description requirement because its original 2004 priority application did not specifically disclose the claimed Gly/Phe-only tetrapeptide subgenus, only a broad group of over 47 million options. Furthermore, the patent failed the enablement requirement, as using any drug moiety in the ADC required undue trial-and-error discovery to confirm its necessary functionality. Consequently, the patent was deemed invalid, and the findings of willful infringement and the damages award were vacated.

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