Canada: U.S. Supreme Court Holds Medical Diagnostic Process Patent Ineligible For Claiming Unpatentable Laws Of Nature

Last Updated: April 30 2012
Article by Peter S.L. Wong

On March 20, 2012, the United States Supreme Court decided Mayo Collaborative Services v. Prometheus Laboratories, Inc., No. 10-1150 (Prometheus), unanimously holding that a particular medical diagnostic process claimed was ineligible for patent protection.

More broadly, Prometheus provides the Court's latest guidance on the boundary between patent-eligible process claims and patent-ineligible natural laws, physical phenomena and abstract ideas.

Prometheus was the exclusive licensee of two patents1 containing claims generally directed to a method of optimizing therapeutic efficacy for treatment of an immune-mediated gastrointestinal disorder comprising two steps: (a) administering one of a class of drugs (thiopurines) and (b) determining the level of a specified metabolite, wherein a level below a specified lower threshold indicates a need to increase the amount of the drug subsequently administered, and a level above a specified upper threshold indicates a need to decrease the amount of the drug subsequently administered.

Prometheus sued Mayo for infringement of the two patents. Mayo filed a motion for summary judgment to declare the patents invalid for improperly claiming natural laws. On appeal, the Supreme Court held that the patents were invalid because "the steps in the claimed processes (apart from the natural laws themselves) involve well-understood, routine, conventional activity previously engaged in by researchers in the field."

Legal Background

The United States Patent Act, §101, defines patent-eligible subject matter to include "any new and useful process", but the Court has long recognized that §101 impliedly excludes natural laws, physical phenomena and abstract idea. This being said, all inventions rely to some extent on natural laws, and so a process is not patent-ineligible merely because it recites a natural law. The difficulty is in determining whether a process claim effectively seeks patent protection for the natural law itself, especially when the process is not tied to a particular machine or apparatus. Prior to Prometheus, a series of Supreme Court decisions2 provided guideposts for assessing patent-eligibility, as follows:

  • the patentee cannot evade the exclusionary principle by either simply limiting the use of a natural law to a particular technological environment, or adding an insignificant step to the application of the natural law;
  • the transformation and reduction of an article to a different state or thing is a clue to the patentability of a process claim that does not include a particular machine, but satisfying this "machine-or-transformation test" is not a necessary requirement;
  • when assessing the patent-eligibility of a process claim, the steps of a claim must be considered as a whole, and the novelty of the steps either in isolation or in combination is not relevant.

The Court's Decision

In Prometheus, the Court characterized the precise relationship between the metabolite concentration and the effectiveness or toxicity of the thiopurine drug to be a natural law. This was because the relationship existed independently from any human action. Proceeding on this basis, the Court considered the discrete issue to be whether the process claims "add enough to their statement of the correlations to allow the processes they describe to qualify as patent-eligible processes that apply natural laws."

To address this issue, the Court analyzed the steps of the process claim, both in isolation and in combination. With respect to the "administering step", the Court stated "doctors used thiopurine drugs to treat patients suffering from autoimmune disorders long before anyone asserted these claims". With respect to the "wherein step", the Court stated that it simply informed doctors about the relevant natural law, while trusting doctors to use those laws appropriately where they are relevant to their decision making. With respect to the "determining step", the Court stated that "methods for determining metabolite levels were well known in the art". With respect to the steps viewed as a whole, the Court stated that the steps "add nothing significant beyond the sum of their parts taken separately." Accordingly, the Court concluded that the claims were patent-ineligible.


For inventors and other parties interested in seeking or challenging patent protection in the United States for process claims, particularly for medical diagnostic tests, the Prometheus decision provides the additional guideposts for assessing patent-eligibility, as follows:

  • patent-eligibility is the threshold issue for patent validity, that precedes issues of novelty, obviousness and adequacy of the specification;
  • in a departure from the Court's past statements, it is permissible to consider the novelty or obviousness of the claimed steps, both in isolation and in combination, when determining patent-eligibility;
  • the exclusionary principle is less likely avoided when a process claim simply adds conventional steps at a high level of generality to natural laws in the abstract, than when a process claims includes unconventional steps that achieve a specific useful result in a unitary manner;
  • the machine-or-transformation test is neither a sufficient nor necessary criterion for patent-eligibility.

The full impact of the U.S. Supreme Court's decision in Prometheus will only be appreciated as trends in its application emerge by the lower courts against patent documents with process claims that recite natural laws not tied to a particular machine or apparatus.

In the absence of a positively stated test, considerable uncertainty may continue to surround the patent eligibility of such process claims. It would seem, however, that the Prometheus decision tends to narrow the threshold of patent-eligibility. Indeed, a lower court relied on the Prometheus decision only 10 days after it was released to invalidate a patent relating to a system, method and computer program for guiding the selection of therapeutic treatment regimens for complex disorders.3

At the very least, the Prometheus decision suggests the need for a fresh consideration of the patent-eligibility of these types of process claims.


1 U.S. Patent No. 6,355,623 and U.S. Patent No. 6,680,302.

2 See: Gottschalk v. Benson, 409 U.S. 63 (1972); Parker v. Flook, 437 U.S. 584 (1978); Diamond v. Diehr, 450 U.S. 175 (1981); and Bilski v. Kappos, 561 US __, (2010).

3 Smartgene Inc. v. Advanced Biological Laboratories, SA (D.D.C 2012).

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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Peter S.L. Wong
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