The United States Court of Appeals for the Federal Circuit has denied Eli Lilly and Company's petition for rehearing en banc in Teva Pharmaceuticals International GmbH v. Eli Lilly and Company, No. 2024-1094, leaving intact a precedential panel decision that reversed the district court's invalidation of Teva's headache-treatment patents. The denial solidifies a distinction between method-of-treatment claims and composition claims for the written description and enablement requirements of 35 U.S.C. § 112(a), with potentially significant implications for life sciences patentees asserting genus-based method claims.

As discussed in detail in our previous article, on April 16, 2026, a Federal Circuit panel reversed the District of Massachusetts's grant of judgment as a matter of law ("JMOL") invalidating three Teva patents (U.S. Patent Nos. 8,586,045; 9,884,907; and 9,884,908). These "headache patents" claim methods of treating headache by administering humanized anti-CGRP antagonist antibodies, the technology underlying Teva's Ajovy® and Lilly's competing Emgality® products.

The panel reinstated a $177 million jury verdict finding that Lilly willfully infringed the headache patents and failed to prove the asserted claims invalid for lack of written description or enablement.

The Panel's Key Holdings

Written Description. The panel held that where a claimed method involves a "well-known genus that is not, itself, the invention," the written description requirement is satisfied when the specification, read in light of the background knowledge in the art, conveys to a person of ordinary skill that the inventor had possession of the claimed method. The record showed the genus of humanized anti-CGRP antagonist antibodies was well known and that any species would perform the claimed function.

Enablement. On enablement, the panel concluded that the relevant "research assignment" for method-of-treatment claims is whether humanized anti-CGRP antagonist antibodies treat headache, not whether a skilled artisan could make or identify every possible member of the antibody genus. Because it was undisputed that a reasonable jury could find all such antibodies would work to treat headache, the enablement requirement was met. The panel characterized the effort to "find or make all" antibodies in the genus as "more akin to extra credit than a necessary research assignment left to others to complete."

The En Banc Petition and Denial

On June 17, 2026, Eli Lilly filed a petition for rehearing en banc, arguing that the panel decision "opens a truck-sized hole in enablement and written description law" and conflicts with the Supreme Court's holding in Amgen Inc. v. Sanofi, 598 U.S. 594 (2023). Lilly presented two questions:

1. Whether adding functional method-of-use limitations to otherwise non-enabled genus claims renders the claims enabled.
2. Whether a specification's disclosure of species outside the scope of a claimed genus constitutes a disclosure of representative species that can provide written-description support for an otherwise unsupported genus claim. 

Several parties filed amicus briefs supporting rehearing, including Merck Sharp & Dohme LLC, Ipsen Biopharmaceuticals, Inc, Amgen Inc., Sanofi S.A., Johnson & Johnson, and Nagra USA LLC.

In opposition, Teva argued that the case involves "(1) novel method of treatment claims, (2) a genus of antibodies that Lilly itself characterized as already 'well known' in the art, and (3) a specification that teaches a POSA that all members of that well-known genus will work in the claimed method of treatment." Teva emphasized that the panel's decision turns on its specific facts and leaves existing precedents intact.

The Federal Circuit has now denied the petition, declining to revisit the panel's analysis. The deadline to file a petition for a writ of certiorari in the United States Supreme Court is December 29, 2026.

Practical Implications

The denial of en banc review has several notable consequences for patent practitioners:

• Method claims may survive where composition claims fall. Teva's antibody composition patents were invalidated in IPR proceedings, but its method-of-treatment claims, covering the same genus of antibodies, survived. Patent holders should consider layered claiming strategies that include method claims as an independent line of defense.
• Prior art knowledge can support § 112 validity. Lilly's own statements in the IPRs that anti-CGRP antibodies were "well known" and "replete" in the prior art were used against it to establish that the genus was sufficiently described and enabled for the method claims. Litigants should be mindful that positions taken in parallel proceedings may be used against them.
• The "well-known genus" framework has been solidified. When the claimed invention is a method using a well-known genus (rather than the genus itself), the written description and enablement analyses focus on the method, whether the genus works for the claimed purpose, rather than on structural diversity within the genus.

Lilly may seek certiorari from the Supreme Court. Given the amicus support for en banc review and the interplay with Amgen, this case may attract further attention. We will continue to monitor any developments.