Mayo v. Prometheus: Fire But No Light

Law professors are apt to say "hard cases make bad law" and the U.S. Supreme Court's recent decision in Mayo v. Prometheus Laboratories certainly falls into this category. In a unanimous decision issued on March 20, two patents that Prometheus had sought to enforce against Mayo Laboratories were struck down because the Court concluded that the patent claims were directed to natural laws and, hence, not eligible for patent protection. 



The decision, authored by Justice Stephen Breyer, has sent a shockwave through the biotechnology industry because the Court's reasoning may lead to the demise of diagnostic-method patents and remove the financial incentives that are currently propelling the growth of personalized medicine. If Breyer's reasoning is broadly applied, it is also hard to see how any diagnostic or even medical treatment method claim can survive scrutiny. 



The principal claim at issue in the Mayo case recited a first step of administering a drug to a patient and a second step of measuring the level of a particular metabolite in the patient's blood and a "wherein" clause that described a level above which there is a likelihood of harmful side-effects and below which the drug dosage may be ineffective. The claim was drafted this way to cover any supplier of an assay that would measure the particular metabolite. 



The Court found this "wherein" clause to be, in essence, an appropriation of a law of nature and not the sort of thing that should be patentable. Breyer compared the claim to Einstein trying to patent E=MC² or Newton trying to capture the law of gravity in a patent. Relying on a decision from the early days of the age of computers that found claims to a mathematical algorithm to be unpatentable because the claims were "so abstract and sweeping as to cover both known and unknown uses" of the formula, Breyer reasoned that the Prometheus claims would likewise "risk disproportionately tying up the use of underlying natural laws, inhibiting their use in making further discoveries." 



But was the discovery claimed in the Prometheus patent truly an abstract law of nature? The patent solved a known problem, namely selecting the right dosage for a very specific class of drugs that patients metabolize differently. Because of the metabolic differences, a dosage that is good for one patient is not necessarily good for another. The patent claim recited the metabolite levels that were too high and those that were too low — in essence identifying the sweet spot for therapeutic efficacy. This was a practical application of science, not an abstraction like the law of gravity. 



The problem with the Court's reasoning is that every diagnostic invention is at its core a discovery of a natural correlation between a biomarker or other analyte and a medical condition. Historically, the question that governed patentability of diagnostic methods, such measuring prostate-specific antigen as an indicator of prostate cancer or high-density lipoprotein as sign of unheathy cholesterol, has been whether the correlation discovered by the inventor was new and unobvious to one skilled in the art — not whether the correlation embodied a law of nature. How can any diagnostic method claim still be eligible for patent protection if the law now precludes diagnostic methods that rely on a scientific principle or law of nature? Would Breyer prefer diagnostic methods be based on lucky guesses or Ouija board results? 



Though not at issue in the Mayo case, the Court's logic in the Mayo decision also casts a shadow on method-of-treatment claims. For more than 200 years, the U.S. patent laws have allowed patent protection — in the form of method claims — for new and unobvious medical treatments with known drugs or agents. Many other countries do not allow patent claims for human treatment but the U.S. laws do — or did. Congress has from time to time debated the value of allowing method of treatment claims. Several years ago Congress did impose some limitations on surgical methods (requiring that the claims also recite a novel surgical instrument) but Congress did not abolish medical-treatment claims. 



However, the logic of the Mayo decision may put medical treatment claims into the "patent ineligible" category, as well. For example, a claim such as "treating a retroviral infection with an effective amount of AZT" (to paraphrase the famous first AIDS drug patent) could be suspect since it could also be considered to be a claim to a law of nature. AZT works by inhibiting reverse transcriptase, an enzyme necessary to the retroviral replication. The AZT inventors discovered this "law of nature." 



A less ominous reading of the Mayo decision is that the Supreme Court simply felt that there wasn't enough meat in the Prometheus claim and perhaps a more specific recitation of the assay steps would have passed muster. If so, then the decision leaves to the lower courts the dirty work of sorting out how much more specific a diagnostic claim must be. 



This process of leaving it up to the lower courts to divine the meaning of the Mayo case has already begun. A few days after its Mayo decision, the Supreme Court granted a petition to review another hotly contested case involving Myriad Pharmaceutical's patents on isolated breast cancer gene sequences — and then immediately remanded the case back to the U.S. Court of Appeals for the Federal Circuit, from whence it came, to reconsider its decision in light of the Mayo ruling. 



It is most unfortunate that the Supreme Court's decision in the Mayo case only discussed one claim of the Prometheus patents. There were several more specific dependent claims in the Prometheus patents that explained how the assay should be conducted, e.g., by measuring metabolite levels in red blood cells or by use of high pressure liquid chromatography. The biotechnology industry and patent practitioners would have benefited from some explanation as to why these claims were likewise unacceptable. Instead, the Supreme Court just kicked the can down the road.

- Tom Engellenner (adapted from my recent article in the National Law Journal)
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