Federal Circuit Refuses to Consider Disease Variants as Species of a Disease Genus for Method of Treatment Patents

Patents are often granted to methods of treatment for diseases and conditions which can be divided into a variety of subclasses based upon disease sub-type, biological target sub-type, patient sub-population, and the like. Logically, diseases and conditions having subclasses and sub-types can be thought of in terms of genus-species (or genus-subgenus).  However, in its recent decision in United Therapeutics Corp. v. Liquidia Techs., Inc.,1 the Federal Circuit refused to consider a disease variant as a species of a disease genus for purposes related to compliance with the written description and enablement requirements of 35 U.S.C. § 112.  

[A]nalogizing a subset of patients having a variant of a particular disease to traditional genus and species claims is inapt.2

In refusing to apply a genus-species analysis, the Federal Circuit sidestepped the Supreme Court’s landmark decision in Amgen v. Sanofi,3 which focused on the scope of enablement for generic claims.  The Court also avoided its own precedent in Juno v. Kite,4 on written description in the genus-species context.  The Court’s opinion on enablement and written description cites neither the Amgen nor Juno decisions.

The Court’s exclusion of methods of treating diseases/conditions from the framework of a traditional genus-species analysis for purposes of compliance with 35 U.S.C. § 112 – whether considered a new rule or a clarification – is bound to create confusion.  

The Method of Treatment Claims in United Therapeutics

The method of treatment claims in United Therapeutics were directed to a method of treating pulmonary hypertension (PH) by administration of treprostinil delivered in an inhalation device.

The patent specification described five subgroups of pulmonary hypertension (PH):

  • Group 1, pulmonary arterial hypertension (“PAH”); 
  • Group 2, pulmonary venous hypertension, i.e., PH related to left-heart disease; 
  • Group 3, PH associated with disorders damaging the lungs; 
  • Group 4, PH caused by chronic thrombotic or embolic disease; and 
  • Group 5, a miscellaneous category for conditions not fitting into other subgroups.

For those in Group 2, PH arises due to cardiac issues (“postcapillary PH”), while in the other groups, PH is caused by pathologies in pulmonary capillaries (“precapillary PH”), such that Group 2 allegedly would not benefit from the claimed treatment with treprostinil in an inhalation device.

The Court Declines to Treat Disease “Variants” as Disease Species 

The Federal Circuit rejected the argument that the method of treatment claims were invalid under 35 U.S.C. § 112 for lack of enablement and adequate written description for postcapillary PH (Group 2).

In its analysis, the Court refused to conduct a traditional genus-species analysis by considering Group 2 PH as a species within the PH genus.

But analogizing a subset of patients having a variant of a particular disease to traditional genus and species claims is inapt.  It would be incorrect to fractionate a disease or condition that a method of treatment claim is directed to, and to require a separate disclosure in the specification for each individual variant of the condition (here, an individual group of pulmonary hypertension patients) in order to satisfy the enablement and written description provisions of 35 U.S.C. § 112, unless these variants are specified in the claims.6

The Federal Circuit and U.S. PTO have consistently treated claims according to genus-species principles independent of subject matter.  The Federal Circuit has employed a genus-species framework in a wide variety of subject matter areas beyond chemical compounds and embracing subject matter outside the life sciences and the unpredictable arts, including in the context of compliance with Section 112.7  Judge Lourie’s opinion in United Therapeutics does not cite to any precedent for the disparate application of genus-species principles according to subject-matter, or for the conclusion that analyzing variants of a disease as genus-species is “inapt” to analyzing variants of compounds (or other subject matter) for purposes of full-scope compliance with Section 112.  

Under the rule announced in United Therapeutics, in a method of treatment claim a disease “variant” is not considered a species (or subgenus) of the claimed disease.  In the myriad ways methods of treatment can be claimed, this rule begs for guidance on its scope, or at least on the meaning of the term “variant.”  In United Therapeutics, the claims involved the treatment of pulmonary hypertension among the five known groups, but “variant” could be interpreted to mean that a genus-species analysis is no longer appropriate for claims to methods of treating any disease/condition with multiple etiologies or causes, such as claims reciting methods of treatment based on target types/subtypes or individualized/personalized medicine and claims, reciting methods of treating patient populations/subpopulations.  

Judge Lourie’s opinion creates a caveat for disease variants that “are specified in the claims,” thereby transforming a disease into a “genus” based solely on whether the patentee decides to claim disease variants, and not on any underpinning legal principle.  The opinion is unclear whether those claimed “variants” can be any “variant” or must be those challenged as not enabled or adequately described under Section 112.

As an example, under the new rule in United Therapeutics, a claim to “a method of treating cancer” does not recite a genus of all cancers, and for purposes of full-scope compliance with Section 112 a genus-species analysis is inapt – unless variants are specified in the claims.  The various types of cancer are not considered species of cancer for purposes of compliance with Section 112 – unless they are “specified in the claims,” even if they are identified in the patent specification.

The Court also makes a distinction for methods of treatment which recite efficacy or safety.  Unless a claimed method of treatment recites safety or efficacy, the Court now leaves the issues of enablement and written description for “variants” of the disease to the FDA, noting only that “every claim to a method of treatment of an ailment has refinements.”

Again, because safety and efficacy are not recited in the claims, we need not deal with Liquidia’s arguments. Disease-specific treatment requirements are matters for the FDA and medical practitioners. They are best suited to make these determinations because practitioners are informed by the findings of the regulatory agency to avoid treatment of patients who will not properly respond. And every claim to a method of treatment of an ailment has refinements.  That is, for any given method of treatment claim, there may be a subset of patients who would not benefit from or should not take the claimed treatment. See Oral Arg. at 4:28–4:58, https://oralarguments.cafc.uscourts.gov/default.aspx?fl=22-2217_0503202 3.mp3. That does not mean that such claims are not sufficiently enabled or supported by written description. A subset of unresponsive patients is not analogous to unsupported species in a generic claim to chemical compounds.8

Ultimately, the Federal Circuit stated that compliance with the enablement and written description requirements for method of treatment claims does not require a separate disclosure for each disease variant, “unless the variants are specified in the claims.”

A separate disclosure in the specification for each individual variant of a disease/condition is not required to satisfy the enablement and written description provisions of 35 U.S.C. § 112 for a method of treatment claim unless the variants are specified in the claims.

The Court’s opinion in United Therapeutics lacks important guidance for drafting, prosecuting, and litigating method of treatment claims.  It makes clear only that the patent specification does not need to address every possible disease subtype or non-responsive patient population to satisfy Section 112, but only if those limitations are not “specified in the claims,” and leaves the rest to the FDA and the patent bar to figure out.     


  1. United Therapeutics Corp. v. Liquidia Inc. (Fed. Cir., July 24, 2023); slip opinion at https://cafc.uscourts.gov/opinions-orders/22-2217.OPINION.7-24-2023_2161663.pdf
  2. Id., slip op. at 17.
  3. Amgen, Inc. v. Sanofi, et al. 598 U.S. __ (2023); https://www.supremecourt.gov/opinions/22pdf/21-757_k5g1.pdf.
  4. Juno Therapeutics, Inc. v. Kite Pharma., 10 F.4th 1330 (Fed. Cir. 2021).
  5. Claim 1 from United Therapeutics’ patent is reproduced below.
  6. United Therapeutics, slip op. at 17.
  7. The Federal Circuit has applied genus-species (or genus-subgenus) principles to patent claims across subject matter including to claims other than chemical compounds and biomolecules, such as openings in spinal implants (Synthes USA, LLC v. Spinal Kinetics, Inc., 734 F.3d 1332 (Fed. Cir. 2013)), fiber optic cable (Hologic, Inc. v. Smith & Nephew, Inc., 884 F.3d 1357 (Fed. Cir. 2018); disclosure of a species (a fibre optics bundle) was sufficient written description to support a genus (all light guides)), reclining furniture (Gentry Galler), numerical ranges (see, e.g., Osram Sylvania, Inc. v. Am. Induction Techs., Inc., 701 F.3d 698 (Fed. Cir. 2012)), and others).
  8. United Therapeutics, slip op. at 17.