On December 2, 2025, the Federal Circuit issued two related decisions concerning Seagen’s U.S. Patent No. 10,808,039 (“the ’039 patent”), asserted against Daiichi Sankyo and AstraZeneca in litigation over the antibody–drug conjugate (ADC) Enhertu^® (fam-trastuzumab deruxtecan-nxki). Seagen sells a competing drug, Adcetris^® (brentuximab vedotin). In Seagen Inc. v. Daiichi Sankyo Co., Ltd., Nos. 23-2424, 24-1176 (consolidated) (appealing Case No. 2:20-cv-00337 (E.D. Tex.)), the court reversed the Eastern District of Texas’s denial of Defendant’s request for judgment as a matter of law (“JMOL”), resulting in a finding that all asserted claims are invalid for lack of written description and enablement.

A companion decision, Seagen Inc. v. Daiichi Sankyo, Inc., No. 24-1878 (appealing PGR2021-00030, previously reported PTAB Issues Final Written Decision Finding Seagen’s Adcetris^® Patent Claims Unpatentable), dismissed Seagen’s PGR appeal as moot.

The ’039 patent claims ADCs containing a Gly/Phe-only tetrapeptide linker. The Federal Circuit held that Seagen’s 2004 priority application—disclosing peptide units encompassing over 47 million tetrapeptide species—provided no “reasonably specific” description of the much narrower 81-member Gly/Phe-only subgenus. The court emphasized the absence of “blaze marks” pointing to this subgenus and cited inventor admissions that they had not conceived Gly/Phe-only tetrapeptides before Enhertu^® became publicly known in 2015. As a result, the patent was not entitled to a 2004 priority date, and the 2015 public disclosure of Enhertu^® anticipated the claims.

The court separately held the patent not enabled under Amgen v. Sanofi, finding that because the claims cover ADCs with any drug moiety and require intracellular cleavage, a skilled artisan would have to engage in unpredictable, trial-and-error testing across a vast universe of drug/linker combinations. With no common structural features correlating to the required functional activity, the specification failed to teach how to make and use the full scope of the claimed genus.

Because the Federal Circuit’s decision invalidated the ’039 patent in full, it rendered Seagen’s appeal from the PTAB’s adverse PGR decision moot, and the court dismissed that appeal.

For more information on this and other biologic patent disputes, please visit BiologicsHQ.com.

 

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The authors would like to thank April Breyer Menon for her contributions to this article.