In Prometheus Laboratories, Inc., v. Mayo Collaborative Services, 2008-1403 (September 16, 2009), the Federal Circuit, on first impression, held medical diagnostic claims to be patent-eligible subject matter under the "machine or transformation" test first elucidated in In re Bilski, 545 F.3d 943 (Fed. Cir. 2008). In Bilski, the Federal Circuit held certain claims directed to a "business method" to be invalid under the "machine or transformation" test for lack of patent-eligible subject matter, under 35 U.S.C. §101. The "business method" in question was a method of hedging risks in commodity trading. The business method claims failed the Bilski test because the claimed subject matter was neither tied to a particular machine nor did it transform anything to a different state or thing.

In Prometheus, the plaintiff sued for infringement of U.S. Patent Nos. 6,355,623 and 6,680,302. The claims of both patents are directed to methods for calibrating the proper dosage of thiopurine in a subject (i.e., a patient). Thiopurine is a drug used to treat both gastrointestinal and non-gastrointestinal autoimmune diseases. Calibrating the level of thiopurine administered to a patient is important because the drug metabolites have potentially toxic side effects. The claims at issue required two steps: (a) "administering" the drug to a subject and (b) "determining" the level of the drug's metabolites in the subject. The claims also required in a "wherein clause" that the measured metabolite levels "indicate a need" to modify the level of administered drug to minimize toxicity and maximize efficacy.

The Southern District of California, on motion for summary judgment, held the claims invalid for failing to claim patent-eligible subject matter under 35 U.S.C. §101. The district court held that the "administering" and "determining" steps were merely "correlations" and "necessary data-gathering steps." The district court also held that the "warning step" found in the wherein clause was "only a mental step" because it did not require any adjustment of the dosing levels. Based on this interpretation, the district court found the claims to be directed only to "correlations" between the administered level of the drug and the determined level of the metabolite on the one hand; and whether any adjustment in the amount of the drug administered may be needed on the other. Such "correlations" in the view of the district court were nothing more than "natural phenomena...result[ing] from a natural body process." Natural phenomena are not patent-eligible subject matter. See, Prometheus, Slip Op. at 8 [quoting, Diamond v. Diehr, 450 U.S. 175, 185 (1981)]. As a result, the district court held the claims invalid because the claims would "wholly pre-empt" any use of the correlations in contravention of 35 U.S.C. §101.

The Federal Circuit reversed and held the claims did contain patent eligible subject matter because the "administering" and "determining" steps are indeed transformative under the Bilski test. In addition, the transformations produced by the claimed method are "central" to the purpose of the invention and not some "merely insignificant extra-solution activity" that fails to provide patent eligible subject matter.

According to the Federal Circuit, the administering step was transformative in two separate ways: First, the administration of the drug resulted in a transformation of the "human body" due to the effect of the drug. Second, the administered drug was itself transformed because the drug was metabolized by the body following administration. More profoundly, the Federal Circuit also held that "methods of treatment...are always transformative when a defined group of drugs is administered to the body to ameliorate the effects of an undesired condition."

Likewise, the "determining step" was considered transformative because the step requires "extract[ing] the metabolites" from a sample to determine their concentration. As noted by the Federal Circuit, metabolite levels "cannot be determined by mere inspection," which would otherwise render the step to be merely data-gathering. In actuality, the blood sample, after application of the determining step, is no longer a blood sample because it has been transformed to determine the metabolite levels.

The Federal Circuit also dismissed the proposition that the transformation of a drug into metabolites is an ineligible "natural process" under 35 U.S.C. §101. As the Federal Circuit pointed out, "quite literally every transformation of physical matter can be described as occurring according to natural processes and natural law." Quoting Bilski, the court stated it is "virtually self-evident that a process for a chemical or physical transformation of physical objects or substances is patent-eligible subject matter." At the same time, the court noted that the "physical administration of a drug" to a subject is clearly not a natural process.

Likewise, the Federal Circuit held the focus under Bilski is the claimed "invention as a whole" and not individual claim elements. The district court, in holding the claims invalid focused primarily on the "wherein clause," which it concluded was nothing more than a "mental step." The Federal Circuit acknowledged that a mental step, by itself, is not patent-eligible subject matter per se. However, the claims at issue included the transformative steps of "administering" and "determining," rendering the claims "as a whole" patent-eligible subject matter. The inclusion of a "subsequent mental step" does not negate the patentability of a claim otherwise containing patent-eligible subject matter.


The Prometheus decision provides some much needed clarity on whether medical or diagnostic method claims are patent-eligible subject matter under the Bilski test. Method-of-treatment claims are now clearly patent-eligible subject matter because it is "always transformative when a defined group of drugs is administered to the body to ameliorate the effects of an undesired condition." Likewise, diagnostic method claims are patent-eligible subject matter as long as the claim requires some entity in a biological sample to be determined, which in turn alters the state of the sample being tested. Thus, careful drafting of medical and diagnostic methods claims should ensure the claims encompass patent-eligible subject matter. Naturally, however, with the Supreme Court having recently granted certiorari in Bilski, it is critical to stay tuned to see whether these bright-line parameters will be affected.