On December 7, 2011, the United States Supreme Court heard oral arguments in Mayo Collective Services v. Prometheus Labs., Inc. (Case No. 10-1150), a case with potentially far-reaching implications for the patentability of methods of medical diagnosis and treatment.


Prometheus is the exclusive licensee of U.S. Patents 6,355,623 and 6,680,302, which are directed to methods of optimizing autoimmune drug therapy by maintaining metabolites of the drugs within a specified range in the blood. Specifically, some of the claims at issue include steps for (1) administering a drug, and (2) determining the level of metabolites in the blood of the subject, while others recite the second step but not the first. The claims recite that a metabolite concentration below a specified threshold “indicates a need” for an increased dose of the autoimmune drug, while a metabolite concentration in excess of a specified ceiling “indicates a need” to reduce the dosage due to possible toxicity. Prometheus developed and marketed an assay for the metabolites of these drugs. Mayo Collective Services initially purchased Prometheus’s test, but decided to develop its own assay in 2004.

Prometheus sued Mayo for patent infringement, and the District Court for the Southern District of California granted summary judgment of invalidity to Mayo based on a finding of patent ineligibility under Section 101 of the Patent Code.1 The United States Court of Appeals for the Federal Circuit reversed. However, this decision was vacated and remanded for reconsideration by the Supreme Court in light of its ruling in Bilski v. Kappos, 130 S. Ct. 3218 (2010), which held that the Federal Circuit’s longstanding “machine-or-transformation” test was not the exclusive test for the patentability of processes.2 On remand, the Federal Circuit held that the administering and determining steps of the claims were necessarily transformative and therefore patentable.3 The Supreme Court granted a second writ of certiorari to determine if a claim which “effectively preempts all uses of naturally occurring correlations” is patentable.

Oral Arguments

It is well known that under U.S. patent laws, claims directed to nature, natural phenomena and abstract ideas are not patentable.4 Mayo has argued that because Prometheus’s claims culminate with an open-ended mental step (the comparison of the metabolite test results with the specified limits of the optimal range), their practical effect is to preempt all uses of the correlation between metabolite levels of these drugs and health, which, according to Mayo, is a naturally occurring phenomenon. Mayo described the process steps as token and conventional data-gathering, well known and long-prevalent in medical practice.

In response, Prometheus argued that the preemption caused by its claims was narrowly limited to a specific and transformative physical process that employs synthetic drugs and machines. Prometheus maintained that the traditional machine-or-transformation test, while not the exclusive test after Bilski, still provides an important clue to patentability because it distinguishes abstractions from real-world processes. Moreover, Prometheus argued, if the synthetic drugs themselves are patentable, specific uses of the drugs must also be patentable. With regard to Mayo’s argument that the process steps of the claims are well known, Prometheus argued that novelty is not an appropriate consideration for Section 101 purposes.

The Justices generally appeared skeptical of Mayo’s argument that the claims were too broad to be patentable because they claimed all practical uses of the correlation of metabolite levels and health. Justices Scalia and Kennedy also seemed doubtful that the subject matter of the patents concerned a natural phenomenon at all, but Justice Breyer was apparently convinced that a natural phenomenon was involved, and Prometheus ultimately conceded the issue.

Justice Breyer took the lead in questioning the parties, likely because of his familiarity with the issues as the dissenting opinion from the dismissal of certiorari in the LabCorp case in 2006, which concerned similar claims.5 The key issue for the Justices, and Justice Breyer in particular, was how much real-world application must be added to a process claim relating to a fact existing in nature before the patent claims a way to use the fact instead of claiming the fact itself. The Justices sought to identify a limiting principle for patentability based on the process steps of the claims, rather than the underlying subject matter. To that end, Justice Breyer and Chief Justice Roberts repeatedly attempted to clarify the matter by questioning counsel about examples of simplified hypothetical patent processes.

Mayo argued that an additional treatment step based on the results of the “determining” step would make the disputed process patentable. The practical significance of such a step is that it makes the patent very easy to avoid, as the infringing steps need not be carried out by a single actor. While Justice Kagan focused on this treatment step for a limiting principle based on the process itself, Mayo argued that this step would make the process patentable by narrowing the scope of preemption of the claims. Prometheus responded that the claims do not recite a treatment step because doctors do not practice according to hard and fast rules, suggesting that such a treatment claim might be of little value.

The Solicitor General of the United States, representing the U.S. Patent and Trademark Office, which supported broad patentability of process claims, argued that the process at issue should be considered patent-eligible but may not be novel. Justice Ginsburg and Chief Justice Roberts seemed inclined to import novelty and obviousness inquiries into the Section 101 analysis, as suggested by several amici for Mayo. During Mayo’s arguments, however, Justices Scalia and Breyer appeared to emphasize the position that novelty was a distinct issue unrelated to the dispute over patent subject matter eligibility under Section 101.

The Justices had far fewer questions for Prometheus than for Mayo. Justice Breyer reiterated his request for a limiting principle based on process specificity. Prometheus, invoking the Bilski case and the O’Reilly v. Morse case, responded that the key inquiry here is the preclusion of follow-on inventions, which, Prometheus argued, is bound to be an imprecise analysis due to the difficulty of predicting technological developments.6


Notably, Justice Breyer indicated during oral arguments that he has reconsidered his LabCorp dissent. He further suggested that he believes that the claims at issue in that case, which are directed to assaying levels of a naturally occurring blood marker and correlating elevated levels of the marker with vitamin deficiency, apply rather than claim the correlation between the marker and the deficiency. If the claims in LabCorp are considered patentable, one would expect that Prometheus’s claims, which are comparable in breadth, or arguably narrower, would also be patentable. It remains to be seen, however, whether Justice Breyer’s view will be reflected in the opinion of the Court or a dissent.

A successful outcome of this appeal for Mayo could lead to the invalidation of many patents directed to diagnostic methods. In the short term, this might result in reduced health care costs and the availability of otherwise infringing diagnostic services.

Such a result, however, may threaten the nascent personalized medicine industry, which arguably requires the patent incentive to discover and market correlations existing in nature between biomarkers and disease states like those at issue in this case and LabCorp. The projected benefits to health and the cost of healthcare from personalized medicine may outweigh the short-term advantages associated with the invalidation of patents to diagnostic methods.

The Court’s opinion in this case will issue later this year.