Precedential and Key Federal Circuit Opinions

1. ENANTA PHARMACEUTICALS, INC v. PFIZER INC. (2025-1427, 6/23/2026) (Lourie, Bryson, Chen)

Lourie, J.  The Court affirmed the district court’s grant of summary judgment that the claims of the asserted patent are invalid as anticipated by a public disclosure of a compound within the scope of the claims.  The issue in this appeal was whether the disclosure of —NHC(O)—C₂-C₁₂-alkyl in a provisional application from which the asserted patent claimed priority provided adequate written description support for —‍NHC(O)—C₁-alkyl disclosed and claimed in the asserted patent.  There was no dispute the intervening public disclosure of a compound having a —NHC(O)—C₁-alkyl group anticipated the asserted patent if it was not afforded the earlier priority date of the provisional application.

The Court concluded the provisional application did not convey to a skilled artisan that the inventors possessed —NHC(O)—C₁-alkyl.  The provisional application’s disclosure of a range of C₂ to C₁₂ provided no support for the asserted patent’s disclosure of C₁ because the provisional application explicitly included an alkyl group with two to twelve carbon atoms (i.e., —NHC(O)—C₂-C₁₂-alkyl), and notably did not include an alkyl group with one carbon atom (i.e., —NHC(O)—C₁-alkyl).  The Court explained that a disclosure of one chemical compound, or integer in this case, cannot necessarily be a disclosure of another, even one close by structurally.  Although patent owner’s expert pointed to purported inconsistencies within the provisional application to opine that the C₂ in —‍NHC(O)—C₂-C₁₂-alkyl was likely to have been a typographical error, there was nothing in the disclosure of —NHC(O)—C₂-C₁₂-alkyl in particular to show that a skilled artisan would understand the disclosed C₂-C₁₂ alkyl to provide support for C₁ alkyl.

 2. IRONBURG INVENTIONS LTD. v. VALVE CORP. (2024-2088, 6/18/2026) (Chen, Hughes, Stark)

Hughes, J.  The Court reversed the district court’s ruling that the defendant was estopped under 35 U.S.C. § 315(e)(2) from asserting two invalidity grounds, which had not been included in the defendant’s prior IPR petition.  The Court concluded that the district court relied on insufficient evidence to estop one ground based on one reference and failed to adequately account for hindsight bias in estopping the other ground based on the combination of the three references.

In a previous appeal, the Court had held that the district court erred by placing the burden of proof on the defendant to show that it could not reasonably have raised certain grounds in its IPR petition.  The Court held that the burden of proof instead rests with the patentee to prove that the defendant reasonably could have raised those grounds during the IPR.  The Court further held that “an IPR petition ‘reasonably could have raised’ any grounds that ‘a skilled searcher conducting a diligent search reasonably could have expected to discover.’”  The Court remanded for the district court to evaluate whether patentee could meet its burden to prove that the defendant “reasonably could have raised” its invalidity grounds.  On remand, the district court again granted patentee’s motion for IPR estoppel. 

In reversing the district court, the Court explained that the IPR estoppel statute “requires a focus on what reasonably, rather than possibly, could have been raised prior to the filing of a relevant IPR petition.”  The Court held that “something more is required for estoppel” than the evidence here that a skilled searcher would have undertaken a classification search that yielded an unreviewable number of search results.  The Court also found that evidence presented by patentee that it had asked a search company to perform searches for prior art was tainted by hindsight.

Judge Stark joined the opinion in full and wrote separately to explain his view that “a patentee relying on the skilled searcher test to estop a challenger, pursuant to § 315(e)(2), from pressing a particular ground of invalidity in district court, must prove at least the following: (i) the prior art reference(s) at issue were findable by a skilled searcher conducting a diligent search and (ii) the skilled searcher also reasonably would have been expected to discover, based on the reference(s) found, the invalidity ground the challenger seeks to assert in court.”  Judge Stark explained that this case centered on the first step of this analysis (i.e., whether the references were reasonably findable), and that the defendant did not separately challenge the second step (i.e., whether, even if all of its references were findable, the grounds for invalidity were somehow not reasonably discoverable). 

 3. A.L.M. HOLDING CO. v. ZYDEX INDUSTRIES (2025-1317, 5/19/2026) (Chen, Cunningham, Stark)

Chen, J.  The Court reversed a district court decision dismissing a patent infringement suit for lack of constitutional standing because the plaintiff retained an exclusionary right sufficient to satisfy the minimum requirement for constitutional standing.

Before this lawsuit, the plaintiff had granted a licensee an “exclusive,” “royalty-bearing, worldwide license” to “manufacture, have manufactured, import, use, sell, offer to sell and otherwise commercialize Licensed Products.”  The plaintiff retained certain rights, including the right to share control of any infringement suit in the case of third-party infringement and an equal split of any costs and damages recovered if the parties decided to jointly pursue legal action.  If either plaintiff or exclusive licensee elected not to pursue infringement, the other party was permitted to bring suit independently.  The license agreement also limited the exclusive licensee’s ability to sublicense patent rights, requiring the plaintiff’s prior approval of the terms and conditions of any sublicense.  After the plaintiff sued the defendant, the district court concluded that the plaintiff lacked constitutional standing to pursue the infringement suit.

As an initial matter, the Court clarified that the constitutional standing inquiry, which asks whether the plaintiff has suffered a constitutionally cognizable injury, is distinct from the separate question of statutory standing, which asks whether the plaintiff qualifies as a “patentee” entitled to sue for infringement—typically by determining whether, in the case of a patent owner, it has transferred away, or in the case of a licensee, it has been transferred “all substantial rights” in the asserted patents.  Although the two standing inquiries are distinct, the same facts bearing on whether a patent owner has granted “all substantial rights” to a licensee to enable the licensee to have statutory standing may also bear on whether the patent owner retained “an exclusionary right” sufficient for constitutional standing.  Thus, cases analyzing statutory standing can be instructive for constitutional standing. 

In this case, the Court concluded that the plaintiff’s retained rights as a patent owner—including the right to sue, right to veto sublicenses, and royalty interests—confirmed that plaintiff retained an exclusionary right sufficient to establish constitutional standing.  The Court explained that because the exclusive licensee could not sublicense the asserted patents free from the plaintiff’s consent and royalty interests, the plaintiff’s retained right to sue was not illusory.  The Court rejected the defendant’s argument that the plaintiff’s right to sue was not exclusionary because the plaintiff could not end a lawsuit by granting a license, finding that the plaintiff had other means by which to settle litigation, including monetary payments or an agreement by an infringer to cease practicing the patents. 

 4. ACTELION PHARMACEUTICALS LTD. v. MYLAN PHARMACEUTICALS INC. (2024-1641, 5/13/2026) (Reyna, Taranto, Stoll)

Taranto, J.  The Court affirmed the district court’s ruling that the defendant does not literally infringe the asserted patents and that the patentee was barred from asserting, and had not proved, infringement by an equivalent.

The asserted patent claims required that the pharmaceutical composition be “formed from a bulk solution having a pH of 13 or higher.”  The district court, after considering both intrinsic and extrinsic evidence, construed “a pH of 13 or higher” to mean “a pH of 12.98 or higher.”  The district court determined that the limitation refers to a pH measurement taken at standard temperature (i.e., 25±2°C) and thus found no literal infringement because it was undisputed that defendant’s bulk solution, when measured at the standard temperature of 25±2°C, has a pH well below 12.98.  The patentee argued that the district court’s standard-temperature construction was incorrect because a relevant artisan would understand that pH should be measured at the refrigerated “operating temperature” of the solution, and defendant’s bulk solution, if measured at that cold temperature, has a pH of above 13.  The Court found that the specification supports the standard-temperature construction because the specification’s definition of “an alkaline environment” as one with “pH>7” is accurate only at standard temperature, the reported results in the specification are most reasonably understood as indicating use of a uniform approach to measuring pH, and the experts agreed that the vast majority of the pH measurements described in the specification refer to standard-temperature values.  The Court also found that the district court properly relied on extrinsic evidence—specifically, the United States Pharmacopeia, which both parties agreed is an important set of standards in the pharmaceutical industry—to find that those skilled in making pharmaceutical compositions, when referring to pH, mean a measurement at standard temperature unless they indicate otherwise.  

Further, the Court concluded that the patentee was estopped from asserting the doctrine of equivalents.  First, prosecution history estoppel barred reliance on doctrine of equivalents because the pH limitation was narrowed during prosecution and the prosecution history demonstrated that the examiner viewed pH 13 as the threshold for which unexpected results, necessary for nonobviousness here, had been shown.  Second the disclosure-dedication rule independently barred patentee’s theory of infringement by an equivalent because the specification disclosed, but the patentee did not claim, sub-13 pH ranges as alternatives to the limitation requiring “a pH of 13 or higher.”