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The diagnostic patent pendulum:

Guideposts for patent eligibility

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A patent directed to a medical diagnostic testing procedure in a human being recently has been invalidated by the Supreme Court in its decision in March in Mayo v. Prometheus. This decision affects the status of claims in patents and pending application in the field of diagnostic testing and, particularly, personalized medicine, such as claims to methods of selecting patients for treatment with a specific drug, and methods of monitoring and assessing efficacy of treatment as it progresses.

Such methods are grounded in discoveries of parameters that correlate an activity of a drug in a patient with a treatment outcome upon which treatment decisions can be made. It is this type of claim that was at issue in Mayo v. Prometheus.

The claims in the patent at issue in Mayo v. Prometheus included steps of: testing patients administered with a thiopurine drug for levels of a metabolic byproduct of the administered drug; and associating the measured levels of the metabolite to a particular treatment decision regarding dosage. The claims, however, did not include implementation of the correlation, so that any medical professional who measures the level of these known metabolites could be alleged to infringe the claim.

It was argued, and the Supreme Court found, that the claim recited nothing more than what occurs in the patient, which is a law of nature. The Supreme Court reasoned that the conversion of the administered drug to its metabolites was a natural process, and that the discovery of this process was no different from the discovery of any law of nature, such as Newton’s laws, which are not patentable subject matter.

The Supreme Court stated that affirmative steps of “administering” a drug to a patient and “measuring” levels of the metabolites, which are not themselves laws of nature, did not save the patent because these steps were conventional.

This decision provides guidance regarding what may not be patentable, and provides limited guidance regarding what is patentable. The U.S. Patent Office, whose rules, while not binding, will be the barrier encountered by patent applicants, has stated that a claim that includes steps that encompass a law of nature should include other elements so that the “claimed process amounts to significantly more than a law of nature, a natural phenomenon, or an abstract idea with conventional steps specified at a high level of generality appended thereto.” Absent legislative intervention by Congress, future litigation will provide more detailed guidance.

The patent practitioner, however, should be careful to draft patent applications that support an array of claims, including claims that include at least an additional step that implements any claimed measured “natural” correlation for a specific or particular purpose or in a non-conventional manner. In addition, since the law is in flux, and applications can take years to prosecute and often are filed in numerous jurisdictions with different standards, applications should include claims that embody a newly discovered correlation.

Submitted by Karen G. Potter and Stephanie Seidman, McKenna Long & Aldridge LLP

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