On December 17, 2010, the Federal Circuit issued its decision in Prometheus v. Mayo sustaining the patentability of Prometheus’s medical treatment claims.[1] The Federal Circuit held that Prometheus’s methods of treatment claims did not encompass laws of nature or preempt natural correlations, and thus, were drawn to patent-eligible subject matter. As part of its determination, the Federal Circuit employed the machine-or-transformation test as a useful and important tool for determining patentable subject matter. Using the test, the Federal Circuit found that the patent’s claimed steps of “administering” and “determining” involved transformations that were central to the claimed invention and that the steps were not insignificant, post solution activity. This decision clarifies standards of patentability of patent claims directed to methods of treatment likely recite patent-eligible subject matter.


Prometheus’s patent claims cover methods of calibrating the proper dosage of thiopurine, commonly used for the treatment of Crohn’s disease and other inflammatory bowel conditions. Thiopurine compositions are pro-drugs that are broken down by the body into useful active metabolites but that also cause toxic side effects. The therapeutic goal is to maximize benefits while minimizing harmful side effects by adjusting the drug dosage to keep the metabolites at an optimum level. The claimed methods involve (1) administering a drug that results in these metabolites and (2) determining the levels of the metabolites by sampling the patient’s blood.[2] The metabolite level is then compared to pre-determined metabolite levels that are known to be associated with either toxicity or beneficial effects in order to determine whether to increase or decrease the level of the drug.

Procedural History

In 2004, Prometheus sued Mayo for infringement of two patents claiming methods of treatment using thiopurine compositions. At the district court level, the district court granted summary judgment that the method of treatment claims were invalid under 35 U.S.C. § 101 for failure to recite patent eligible subject matter, holding that “the patents claimed the correlations between certain thiopurine drug metabolite levels and therapeutic efficacy and toxicity.”[3] The district court found the claimed correlations to be “natural phenomena” and unpatentable “because the correlation resulted from a natural body process.” The district court further noted that “the inventors merely observed the relationship between these naturally-produced metabolites and therapeutic efficacy and toxicity.” Finally, the district court found that the “administering” and “determining” steps were merely data-gathering steps and that the use of this information to adjust dosage was a mental step.

In September 2009, the Federal Circuit reversed the district court ruling by applying the then exclusive test for statutory patentable subject matter, the machine-or-transformation test: “A claimed process is surely patent-eligible under § 101 if: (1) it is tied to a particular machine or apparatus, or (2) it transforms a particular article into a different state or thing.” The Federal Circuit found that the “administering” and “determining” steps were transformative and not merely data-gathering steps and that the claims did not wholly preempt natural law.[4]

Mayo appealed. During the pendency of the appeal, the Supreme Court issued its opinion in Bilski v. Kappos (Bilski).[5] In Bilski, the Supreme Court reviewed whether claims directed to a method of hedging risk were drawn to patentable subject matter. In deciding the case, the Supreme Court refused to draw any bright-line rules in determining patentable subject matter except those that prohibited patenting abstract ideas, laws of nature or physical phenomena. Instead, the Supreme Court ruled under existing precedent that Bilski’s claims were invalid for attempting to patent an abstract idea. The Supreme Court did not reject the Federal Circuit’s machine-or-transformation test as a whole, but rather, held that the test was not the sole or exclusive test for determining patentable subject matter. The Supreme Court in Bilski, however, did find that the machine-or-transformation test was a “useful and important tool” in determining patent eligibility.

After deciding Bilski, the Supreme Court granted certiorari to Mayo and, simultaneously, vacated and remanded (GVR) Mayo’s appeal of the Federal Circuit’s decision in Prometheus for further consideration in light of the Supreme Court’s decision in Bilski.


In reviewing Prometheus’s claims in light of Bilski, the Federal Circuit first determined that Prometheus’s claims did not fall within one of the categorical exclusions of patent eligible subject matter. The Federal Circuit stated that the central inquiry was whether Prometheus’s claims are “drawn to a natural phenomenon, the patenting of which would entirely preempt its use...”[6] The Federal Circuit answered that question in the negative, holding that Prometheus’s claims recite an application of naturally occurring correlations but that the claims did not preempt the use of those naturally occurring correlations. The Federal Circuit noted that Prometheus’s claims recited specific treatment steps and not just the correlations themselves. The specific treatment steps identified by the Federal Circuit were the administration of a drug and the measurement of specific metabolites. Thus, the Federal Circuit found that “[t]he inventive nature of the claimed methods stems not from preemption of all use of these natural processes, but from the application of a natural phenomenon in a series of steps comprising particular methods of treatment.”[7]

Second, the Federal Circuit found that the claims at issue passed the machine-or-transformation test. Although no longer the exclusive test for patentable subject matter, the Federal Circuit noted the Supreme Court’s acknowledgement that the machine-or-transformation test was “a useful and important tool.” Prometheus’s claims passed the test because method of treatment claims “are always transformative when one of a defined group of drugs is administered to the body to ameliorate the effects of an undesired condition . . .”[8] More particularly, the Federal Circuit held that the step of “administering” a drug was transformative because a drug transforms a body and that the “determining” step was transformative because it involved some modification of the substances to be measured.

Mayo had argued that the “administering” and “determining” steps were merely insignificant, post solution activity. The Federal Circuit disagreed, finding that the recited steps were central to the claimed method, i.e. a method of treatment, and that such steps were not merely data gathering steps because “they are part of treatment regimes for various diseases using thiopurine drugs.”[9]

The Federal Circuit compared Prometheus’s claims to the claims at issue in In re Grams (Grams).[10] In Grams, the claims recited (1) performing a clinical test and (2) determining if an abnormality existed based on the results of the test. In distinguishing Prometheus’s claims, the Federal Circuit noted that “the essence of [Grams’s] claimed process was the mathematical algorithm, rather than any transformation of the tested individuals.”[11] Because the clinical tests in Grams were merely to obtain data and were not transformative, the Federal Circuit found Prometheus’s claims distinguishable from Grams’s claims. The Federal Circuit found that the transformations recited in Prometheus’s claims were not merely data gathering steps because they were in fact transformative and integral to the claimed treatment regimes.

Finally, the Federal Circuit held that although Prometheus’s claims also recited a mental step, such a mental step was not fatal to the claims at issue. The Federal Circuit found that the mental step, i.e. providing a warning based on the results of the tests, did not negate the transformative nature of the “administering” and “determining” steps.


The Federal Circuit found that when analyzing the claimed invention as a whole, answering the question, “What did the applicant invent?,” the answer was: “a series of transformative steps that optimizes efficacy and reduces toxicity of a method of treatment for particular diseases using particular drugs.”[12]

The Federal Circuit’s decision appears to mark an important application of the Supreme Court’s ruling in Bilski. Although the decision is limited to medical treatment claims, it provides an example of the analytical framework that courts are likely to use in future cases where the claimed subject matter is subject to patent eligibility challenges.

[1] Prometheus Lab., Inc. v. Mayo Collaborative Servs. et al., Case No. 2008-1403 (Fed. Cir. December 17, 2010) (Prometheus).

[2] Claim 1 from Prometheus’s U.S. Pat. 6,355,623 is representative:

1. A method of optimizing therapeutic efficacy for treatment of an immune-mediated gastrointestinal disorder, comprising:

(a) administering a drug providing 6-thioguanine to a subject having said immune-mediated gastrointestinal disorder; and
(b) determining the level of 6-thioguanine in said subject having said immune-mediated gastrointestinal disorder,
wherein the level of 6-thioguanine less than about 230 pmol per 8x108 red blood cells indicates a need to increase the amount of said drug subsequently administered to said subject and
wherein the level of 6-thioguanine greater than about 400 pmol per 8x108 red blood cells indicates a need to decrease the amount of said drug subsequently administered to said subject.

[3] Prometheus Labs., Inc. v. Mayo Collaborative Servs., No. 04-CV-1200, 2008 WL 878910 (S.D. Cal. Mar. 28, 2008).

[4] Prometheus Labs., Inc. v. Mayo Collaborative Servs., 581 F.3d 1336 (Fed. Cir. 2009).

[5] Bilski v. Kappos, 561 U.S. --, 130 S. Ct. 3218 (2010).

[6] Prometheus at 12.

[7] Prometheus at 15-16.

[8] Prometheus at 17.

[9] Prometheus at 21.

[10] In re Grams, 888 F.2d 835 (Fed. Cir. 1989)

[11] Prometheus at 20.

[12] Prometheus at 23.

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