Whether a federal court with exclusive jurisdiction over a federal patent-law dispute may abstain in favor of a state court with no jurisdiction over that dispute

QUESTION PRESENTED Pursuant to 28 U.S.C. §1338(a), federal courts have exclusive jurisdiction over all cases arising under federal patent law; that jurisdiction is exclusive of state courts, which are explicitly prohibited from adjudicating such cases. Petitioners brought this suit in federal court seeking a declaration that its products were not covered by valid patent claims and thus they did not owe respondent damages. The district court assumed it had exclusive jurisdiction to hear petitioners’ claims, but “abstain[ed]” from resolving them—deferring instead to a “mirror image” Indiana state-court proceeding respondent had _ brought against petitioners, in which the state trial court essentially held a patent infringement trial, addressing, inter alia, issues of claim construction and PTO cancellation of the same patent claims. On appeal, the Federal Circuit went even further than the district court: It explicitly held in a precedential opinion that the district court had _ exclusive jurisdiction, such that the Federal Circuit (and not the Seventh Circuit) had exclusive appellate jurisdiction. But despite holding that the federal courts had exclusive jurisdiction over this federal patent-law dispute, the Federal Circuit held the district court could properly “abstain” from resolving the parties’ federal patent-law dispute in deference to the ongoing state-court proceedings. The question presented is: Whether a _ federal court with exclusive jurisdiction over a claim may abstain in favor of a state court with no jurisdiction over that claim.