Mayo v Prometheus: Patentable Subject Matter in the US Supreme Court

The case concerned two process patents held by Prometheus for use in medical treatment.  The patents optimised the use of thiopurine drugs to treat certain autoimmune disorders based on whether a patient’s level of thiopurine metabolites fell above or below a specified range.

The Supreme Court held that the subject matter of the patents was not patentable because they involved merely conventional applications of laws of nature.  The Court identified the relevant natural laws as “relationships between concentrations of certain metabolites in the blood and the likelihood that a dosage of a thiopurine drug will prove ineffective or cause harm”.  These relationships “exist in principle apart from any human action”.  The Court made no mention of the fact that quantifying that relationship or applying it to treatment were both unknown in the prior art.

In the Court’s opinion, the measurement and calculation of optimal dosage according to Prometheus’ patents added only well-understood, routine, conventional activity to the laws of nature.  They did not involve the “inventive application” of those laws, or the addition of “other elements or a combination of elements, sometimes referred to as an ‘inventive concept,’ sufficient to ensure that the patent in practice amounts to significantly more than a patent upon the natural law itself.”

The Court gave little further guidance on what additional elements are required in order to constitute patentable subject matter, apart from citing authorities that fell on one side or another of that boundary – such as Gottschalk v Benson (1972), Parker v Flook (1977), and Bilski v Kappos (2010) on the unpatentable side; and Diamond v Diehr (1981) and the UK decision of Nielson v Harford (1841) on the patentable side.  The Court also made a distinction that is perhaps dubious given the particular correlation found by Prometheus:  “Unlike, say, a typical patent on a new drug or a new way of using an existing drug, the patent claims do not confine their reach to particular applications of those laws”.

The decision departs from the trend of decisions in the Federal Circuit and EPO Boards of Appeal, where the requirement of patentable subject matter is a typically lower threshold, satisfied if a law of nature is not claimed as such but is usefully applied.  However, the evident concerns of the Court about whether the patentee’s contribution was inventive or merely routine, as well as the risk of over-broad claims tying up future research, could have been engaged in their more traditional domain as part of the validity assessment for novelty, inventive step and sufficiency.