In 2020, Pfizer’s Seagen accused Japanese rival Daiichi Sankyo of infringing its patent with the cancer drug Enhertu, which Daiichi jointly developed with AstraZeneca. In 2022, a jury found Daiichi liable for patent infringement and awarded Seagen $41.8 million in damages.

On December 2, 2025, the U.S. Court of Appeals for the Federal Circuit sided with Daiichi Sankyo, ruling that Seagen’s patent was invalid because it failed to adequately describe the antibody invention it covered. The court overturned the 2022 infringement verdict issued in Texas.

A Pfizer spokesperson said the company is disappointed with the decision and is considering next steps.

Reference Materials:

https://www.reuters.com/legal/litigation/daiichi-wins-appeal-42-million-us-verdict-enhertu-patent-case-2025-12-02/