Ascendis Pharma A/S v. Biomarin Pharmaceutical Inc.

Court of Appeals for the Federal Circuit·Decided March 26, 2026·No. 26-1026·Published

Opinion

United States Court of Appeals for the Federal Circuit

ASCENDIS PHARMA A/S, ASCENDIS PHARMA GROWTH DISORDERS A/S, ASCENDIS PHARMA, INC.,

Plaintiffs-Appellants

v.

BIOMARIN PHARMACEUTICAL INC., Defendant-Appellee

2026-1026

Appeal from the United States District Court for the Northern District of California in No. 4:25-cv-05696-YGR, Judge Yvonne Gonzalez Rogers.

Decided: March 26, 2026

GABRIEL K. BELL, Latham & Watkins LLP, Washington , DC, argued for plaintiffs-appellants. Also represented by MICHAEL A. DAVID, SARAH ELIZABETH PROPST, JAMIE UNDERWOOD; ROGER J. CHIN, San Francisco, CA; MICHAEL E. JOFFRE, JOHN CHRISTOPHER ROZENDAAL, DEIRDRE M. WELLS, Sterne Kessler Goldstein & Fox PLLC, Washington , DC.

EDWARD R. REINES, Jones Day, Palo Alto, CA, argued for defendant-appellee. Also represented by DANIEL PAUL 2 ASCENDIS PHARMA A/S v. BIOMARIN PHARMACEUTICAL INC.

JOHNSON, Pittsburgh, PA; GASPER LAROSA, New York, NY; SEAN CHRISTIAN PLATT, San Diego, CA; JASON G. WINCHESTER, Chicago, IL.

Before LOURIE, CHEN, and STOLL, Circuit Judges.

STOLL, Circuit Judge.

Under 28 U.S.C. § 1659(a)(2), a respondent in a proceeding before the United States International Trade Commission may seek to stay a district court action involving the same parties and same issues if the request is made within certain specified time limits. A stay under § 1659(a)(2) is mandatory and cannot be lifted until the Commission’s determination becomes final. This appeal asks whether a respondent in an ITC proceeding may seek a mandatory stay of its refiled declaratory judgment action involving the same parties even though it had previously filed a declaratory judgment action and missed the deadline for seeking a stay under § 1659(a)(2). We hold that it may not.

BACKGROUND

28 U.S.C. § 1659(a) states: (a) Stay.—In a civil action involving parties that are also parties to a proceeding before the United States International Trade Commission under section 337 of the Tariff Act of 1930, at the request of a party to the civil action that is also a respondent in the proceeding before the Commission, the district court shall stay, until the determination of the Commission becomes final, proceedings in the civil action with respect to any claim that involves the same issues involved in the proceeding before the Commission, but only if such request is made within—

ASCENDIS PHARMA A/S v. BIOMARIN PHARMACEUTICAL INC. 3

(1) 30 days after the party is named as a respondent in the proceeding before the Commission , or (2) 30 days after the district court action is filed, whichever is later. 28 U.S.C. § 1659(a) (emphasis added).

Ascendis 1 and BioMarin Pharmaceutical Inc. are both drug manufacturers developing treatments for children with achondroplasia (ACH), a genetic condition that causes short-limbed dwarfism. In 2021, BioMarin launched Voxzogo®, a treatment for ACH approved by the Food and Drug Administration. BioMarin’s U.S. Patent No. RE48,267 covers certain C-type natriuretic peptide (CNP) variants, including Voxzogo.

On March 31, 2025, Ascendis filed a New Drug Application (NDA) with the FDA for its drug TransCon® CNP. The next day, on April 1, 2025, BioMarin filed a complaint with the ITC against Ascendis, requesting that the ITC “institute an investigation to remedy the unlawful and unfair importation into the United States, and sale for importation into the United States, of certain drug products containing [CNP] variants . . . that infringe” the ’267 patent. J.A. 1029 ¶ 1. BioMarin alleged that the quantity of Trans- Con CNP that has been “imported exceeds any quantity that would be solely for uses reasonably related to the development and submission of information to the FDA.” J.A. 1041 ¶ 48. Ascendis responded that TransCon CNP has not been approved by the FDA and that it “has not made, used, offered to sell, sold, or imported its TransCon

1 “Ascendis” includes Plaintiffs-Appellants here: Ascendis Pharma A/S, Ascendis Pharma Growth Disorders A/S, and Ascendis Pharma, Inc.

4 ASCENDIS PHARMA A/S v. BIOMARIN PHARMACEUTICAL INC.

CNP into the United States, other than for reasons directly related to obtaining FDA approval.” J.A. 1005 ¶¶ 19–20.

On April 11, 2025, Ascendis filed a complaint for declaratory judgment of non-infringement in the United States District Court for the Northern District of California , asserting, inter alia, that its “manufacture, use, and importation of TransCon CNP” is “exempt from patent infringement liability by the statutory safe harbor” provision in 35 U.S.C. § 271(e)(1). J.A. 2002 ¶ 1; Complaint for Declaratory Judgment, Ascendis Pharma A/S v. BioMarin Pharm. Inc., No. 4:25-cv-03302 (N.D. Cal. Apr. 11, 2025), ECF No. 1 (“Original Complaint”). Over thirty days later, on May 29, 2025, Ascendis moved for a speedy hearing on its safe harbor defense. J.A. 2332. In response, BioMarin moved to dismiss or stay the declaratory judgment action pending conclusion of the ITC’s investigation, which Ascendis opposed. See J.A. 2359; J.A. 2376. Two weeks later, in a full reversal of its position, Ascendis filed a notice of voluntary dismissal without prejudice for purposes of refiling its declaratory judgment action to seek a mandatory stay under § 1659(a)(2). J.A. 2630–31. Specifically, Ascendis explained that it planned to:

[R]e-file a declaratory judgment complaint for non- infringement of [U.S. Patent No. RE48,267], which new action it plans to stay pursuant to the mandatory stay provision of 28 U.S.C. § 1659 in favor of parallel ITC proceedings. Ascendis is filing a new action rather than amending the complaint and moving to stay the instant action in order to avoid any possible dispute about the applicability to the present action (which has been pending for more than 30 days) of the mandatory stay provided by that statute.

J.A. 2631 (emphases added).

That same day, Ascendis filed a new declaratory judgment complaint. J.A. 1001–73 (“Refiled Complaint”). The

ASCENDIS PHARMA A/S v. BIOMARIN PHARMACEUTICAL INC. 5

Refiled Complaint is nearly identical to the Original Complaint except that it pleads non-infringement broadly, which includes the safe harbor defense. Two weeks later, Ascendis filed a motion for a mandatory stay under 28 U.S.C. § 1659(a)(2). J.A. 1077. BioMarin opposed the motion—asserting that Ascendis’s request was untimely— and moved for a discretionary stay under Landis v. North American Co., 299 U.S. 248 (1936). J.A. 1097–1100. On September 19, 2025, the district court granted BioMarin’s motion for a discretionary stay and denied Ascendis’s motion for a mandatory stay as moot. J.A. 4. 2 Ascendis appeals .

DISCUSSION

On appeal, Ascendis asserts that the district court erred in denying a mandatory stay under § 1659(a)(2) and that we have jurisdiction under the collateral order doctrine . Before we can address either question, we must first consider whether Ascendis has Article III standing to bring its appeal before this court.

I

“We review Article III standing, a threshold jurisdictional issue and a question of law, de novo.” Canadian Lumber Trade All. v. United States, 517 F.3d 1319, 1330– 31 (Fed. Cir. 2008) (citations omitted). “Standing must be met by persons seeking appellate review . . . .” Hollingsworth v. Perry, 570 U.S. 693, 705 (2013) (cleaned up). Parties seeking appellate review must show that they

2 The district court provided an updated order to its original order. Its original order can be found at Ascendis Pharma, Inc. v. BioMarin Pharm. Inc., No. 4:25-CV-05696- YGR, 2025 WL 2924225 (N.D. Cal. Sept. 9, 2025), but the updated order is not available on Westlaw. The order was updated to address the parties’ stipulation and provide a typographical correction. J.A. 1 n.1.

6 ASCENDIS PHARMA A/S v. BIOMARIN PHARMACEUTICAL INC.

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