The US Court of Appeals for the Federal Circuit held that a respondent in a US International Trade Commission proceeding may not seek a mandatory stay of a companion federal district court case under 28 U.S.C. § 1659(a)(2) by refiling a declaratory judgment action involving the same parties when it missed the mandatory 30-day deadline for seeking a stay in the originally filed action. Ascendis Pharma A/S v. BioMarin Pharmaceutical Inc., Case No. 26-1026 (Fed. Cir. Mar. 26, 2026) (Lourie, Chen, Stoll, JJ.)

Ascendis Pharma and BioMarin Pharmaceutical are both drug manufacturers. Ascendis filed a New Drug Application (NDA) with the US Food & Drug Administration (FDA) for its drug TransCon CNP. The next day, BioMarin filed a complaint at the Commission, alleging that TransCon CNP infringed a BioMarin patent. To avoid the Commission’s importation safe harbor, BioMarin alleged that TransCon CNP was being imported in a quantity that exceeded “any quantity that would be solely for uses reasonably related to the development and submission of information to the FDA.”

Ascendis filed a declaratory judgment action in federal district court, asserting that its “manufacture, use, and importation” was “exempt from patent infringement liability by the statutory safe harbor.” After BioMarin moved to dismiss or stay the declaratory judgment action, Ascendis reversed course and filed a notice of voluntary dismissal, stating its intention to refile its declaratory judgment action and seek a mandatory stay under § 1659(a)(2). Ascendis refiled and two weeks later filed a § 1659(a)(2) motion for a mandatory stay. The district court granted BioMarin’s discretionary stay and denied Ascendis’s motion as moot. Ascendis appealed.

First addressing appellate jurisdiction, the Federal Circuit held that Ascendis had standing for its appeal. At the district court, BioMarin had argued that the district court should retain authority to lift any stay and stated that if the FDA approved TransCon CNP and the Ascendis NDA, BioMarin intended to seek preliminary injunctive relief from the district court. The Federal Circuit explained that those circumstances created a sufficiently real and immediate controversy for appellate jurisdiction.

The Federal Circuit then assessed whether it had jurisdiction under the collateral order doctrine. Under that doctrine, an order must meet three requirements to permit an interlocutory appeal. It must “(1) ‘conclusively determine the disputed question’; (2) ‘resolve an important issue completely separate from the merits of the action’; and (3) ‘be effectively unreviewable on appeal from a final judgment.’” Because denial of Ascendis’s stay motion conclusively determined that issue, and because the intent of § 1659(a)(2) is to prevent overlapping litigation, the Court found that the requirements for collateral order jurisdiction were met.

The Federal Circuit concluded that Ascendis’s arguments failed on the merits, however. After entering a discretionary stay, the district court had denied Ascendis’s motion as moot. The Federal Circuit found that a temporary stay does not necessarily render a stay under § 1659(a)(2) moot, and that a discretionary stay that can be lifted is not the same as (and thus does not moot) a request for [...]

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