Mayo Collaborative Services v. Prometheus Laboratories, Inc.

LII note: The U.S. Supreme Court has now decided Mayo Collaborative Services v. Prometheus Laboratories, Inc..


Whether the possible “transformations” of body chemistry involved in giving a patient prescription drugs and testing the patient's blood for a naturally occurring correlation are enough to validate a patent for the correlation.

Oral argument: 
December 7, 2011

In this case, the Supreme Court will evaluate the validity of two patents held by Respondent Prometheus Laboratories. Prometheus had marketed a multistep medical test based on these patents, which describe the proper dosage range of powerful immunosuppressive drugs. However, after Petitioner Mayo Medical Laboratories announced its intention to market a competing medical test in 2004, Prometheus sued for patent infringement. Mayo now argues that the patents are invalid because they seek to monopolize a natural phenomenon, preempting all other uses of a naturally occurring correlation between metabolites and patient health. Prometheus, on the other hand, argues that the patents are valid because they involve concrete applications and cover patentable correlations, not just natural phenomena. The decision in this case may affect the cost and quality of patient health care, as well as the incentives for research and development in the medical industry.

Questions as Framed for the Court by the Parties 

Whether 35 U.S.C. § 101 is satisfied by a patent claim that covers observed correlations between blood test results and patient health, so that the claim effectively preempts all uses of the naturally occurring correlations, simply because well-known methods used to administer prescription drugs and test blood may involve “transformations” of body chemistry.


Petitioner Mayo Collaborative Services (“Mayo”) is a for-profit medical laboratory operating within the Mayo Clinic, a charitable institution providing medical education, research, and clinical care. The Mayo laboratory is recognized in particular for its treatment of autoimmune diseases, including gastrointestinal conditions like Crohn’s Disease.

When caring for patients with autoimmune diseases, one treatment option is the administration of thiopurine drugs. However, like all drug treatments, if the prescribed dosage of thiopurine is too low, the patient’s treatment will be ineffective; on the other hand, because thiopurine is a powerful immunosuppressive substance, if the prescribed dosage is too high, it may cause toxic effects in patients.

When a patient takes thiopurine, the patient’s body breaks down the drug into chemicals called “metabolites.” After conducting a study on patients suffering from autoimmune conditions, researchers in a Montreal hospital discovered a correlation between metabolite levels in patients and the optimal dosage range of thiopurine. In 1998, Respondent Prometheus Laboratories (“Prometheus”) licensed the researchers’ results, and subsequently patented them with the United States Patent and Trademark Office.

Prometheus’s patent claims involve two steps: first, an "administering” step, when the thiopurine drugs are provided to patients, and second, a “determining” step, when patients’ metabolite levels are established. Following these steps, the patients’ metabolite levels are compared to fixed recommended metabolite levels, according to which a physician may increase or decrease the prescribed thiopurine dosage. Based on these patents, Prometheus also developed and commercially marketed a metabolite blood test.

Mayo formerly purchased and used Prometheus’s test when treating its autoimmune patients, but in 2004, it decided to develop its own test. The Mayo test used the same methods for administering the thiopurine drugs and for testing the patients’ blood for metabolite levels, but used different fixed recommended levels of metabolites to evaluate possible toxicity in patients. However, after Mayo announced its intent to use the test internally, and to market it to others, Prometheus sued Mayo for patent infringement, delaying the launch of the test.

After ruling at first that Mayo’s test infringed Prometheus’s patents, the United States District Court for the Southern District of California invalidated the Prometheus patents under 35 U.S.C. § 101. The district court found that the patents impermissibly claimed a natural phenomenon, namely, the correlation between metabolite levels and recommended thiopurine dosages. The court also characterized the Prometheus test steps as mere “data-gathering” steps culminating in a mental “warning” step, advising but not actually causing any changes in dosage amounts.

On appeal, and following a GVR order, the United States Court of Appeals for the Federal Circuit reversed the district court, holding that Prometheus’s patents were valid under Section 101. Applying the machine-or-transformation test, the Federal Circuit argued that the Prometheus patent steps went beyond data gathering and mental warnings, but were “transformative”—involving chemical bodily change, as well as transformative metabolite blood testing. Furthermore, because the patents recited specific treatment steps, not just natural correlations, they did not wholly preempt all other uses of the correlations.


Under United States patent law, whoever invents or discovers a new process or machine may obtain a patent for his or her invention or discovery. Petitioner Mayo Collaborative Services argues that Respondent Prometheus Laboratories cannot patent its process of testing blood for thiopurine metabolites because this process consists only of pre-existing, widely practiced medical methods: administering a drug (in this case, the thiopurine class of drugs), examining the blood for metabolites of the drug, and then adjusting the drug dosage if the metabolite level is too high or too low. In response, Prometheus contends that these steps do in fact constitute a patent-eligible “process” under the relevant patenting statute. According to Prometheus, its patents do not preempt all practical uses of observed correlations between the level of metabolites and patient health, since the patent claims are limited to the specific context of autoimmune diseases.

Patentable Process under § 35 U.S.C. 101

Mayo argues that Prometheus’s claims fail to meet the definition of a patentable process set forth in 35 U.S.C. § 101. According to Mayo, merely framing a natural phenomenon within a set of steps that do not modify how the phenomenon occurs does not qualify as a patent-eligible process. In this case, Mayo argues that the first two steps claimed by Prometheus—administering a thiopurine drug and then analyzing a patient’s blood sample—are purely “data-gathering” steps that set no limits on Prometheus’s claim to the natural correlation between metabolite levels and patient health. Further, Mayo contends that Prometheus’s patents do not meet the Supreme Court’s machine-or-transformation test, which defines “transformation” as the physical conversion of a thing from one state to another. Mayo maintains that Prometheus’s claimed process fails that test because the sole transformations involved—the thiopurine break-down and the blood analysis—relate only to these broad data-gathering steps.

Additionally, Mayo asserts that its arguments against Prometheus’s patent claims rest squarely on the language of Section 101, which requires that a patentable claim be “new” and “useful.” According to Mayo, Congress did not intend to change the substance of patent law through the 1952 Patent Act, which merely modernized the eighteenth-century language requiring a patent to relate to a “new and useful art”; thus, some initial analysis of whether the patent covers a “new” and “useful” process must apply. Mayo emphasizes that Prometheus’s claim to the first two steps of its process—drug administration and blood testing—cannot be “new” because they already existed in medical practice. Furthermore, in Mayo’s view, this analysis does not exceed Section 101’s threshold inquiry, nor does it reach the subsequent patentability requirements of novelty and non-obviousness under Sections 102 and 103 of the Patent Act. Therefore, because Prometheus is situating a natural correlation within steps constituting a pre-existing, widespread medical practice, Mayo argues that Prometheus’s patents are not a new and useful process as required under Section 101.

In response, Prometheus contends that its patents do comprise a “process” under Section 101 because the patents entail actual, concrete applications of scientific principles, and are not limited to an abstract correlation between the level of thiopurine metabolites and patient health. The patents, according to Prometheus, do not cover basic and unalterable natural laws, such as the law of gravity or the Pythagorean Theorem; rather, the patents concern the manipulation of physical material for a calculated end—thus involving concrete applications rather than mere abstract principles. Prometheus asserts that, since its patents specify particular processes needed to use the thiopurine metabolite correlation, the patents are valid under the machine-or-transformation test. Prometheus claims that the first two steps in its patents are not mere “data-gathering,” but must be analyzed in the context of the patents as a whole, in which drug administration and blood analysis are necessary to facilitate the subsequent steps of actual patient treatment.

Furthermore, according to Prometheus, by arguing that the patents are invalid because the first two steps rely on pre-existing methods and technologies, Mayo is blending the threshold question of patent eligibility under Section 101 with the novelty and non-obvious provisions contained in Sections 102 and 103 of the Patent Act. In particular, Prometheus asserts that Mayo’s emphasis on the phrase “new and useful” in Section 101 is misplaced, since Congress did in fact intend to separate the novelty and non-obviousness standards from threshold patent eligibility when it modified the statute’s language in 1952. Prometheus contends that the questions raised by Sections 102 and 103 are not currently present before the Court, and therefore the Court’s analysis must focus solely on whether Prometheus’s patents constitute a “process.” Prometheus asserts that to reach Sections 102 and 103 now would be premature, and would not give Prometheus a chance to fully present its evidence that the patents meet statutory standards. Thus, Prometheus argues that its patents are valid under Section 101 because they delineate a process for improving patient health based on metabolic transformations.

Preemption of Natural Phenomena

According to Mayo, Prometheus’s patent claims violate Section 101 because they impermissibly preempt the use of a natural phenomenon. Mayo notes that the correlations between thiopurine metabolite levels and the health of a particular patient are determined solely by the human body’s natural break-down of the drug into metabolites. Hence, because these correlations are produced by inherent biological processes, Mayo contends that Prometheus cannot be said to have “invented” the correlations, and is therefore prevented from including them in its patents. In addition, Mayo argues that the final, mental step of Prometheus’s process—determining whether the patient’s actual metabolite level is within the range specified by Prometheus’s patent claims—is so broad as to preempt all practical use of the correlation. Mayo asserts that, under Prometheus’s patents, no healthcare provider can observe the metabolite level and decide how to adjust the patient’s dosage without infringing the patents. Furthermore, according to Mayo, since researchers would have to abandon simple blood testing and invent a new, cumbersome test to get around Prometheus’s patents, the patents have the practical effect of privatizing a natural phenomenon, an impermissible outcome under Supreme Court precedent.

However, Prometheus responds that patent-ineligibility claims should be considered carefully, because all methods and processes can be reduced to natural phenomena. According to Prometheus, its patents do not preempt all uses of natural phenomena since, like the rubber-curing process the Court found patentable in Diamond v. Diehr, Prometheus’s patents cover only a narrow range of scientific knowledge. Further, Prometheus argues that its patent claims do not preempt all uses of the natural correlations because the patents have a narrow focus—determining thiopurine metabolite levels with respect to patients who suffer from autoimmune diseases. Prometheus argues that the prohibition on patenting natural phenomena applies to only the most basic scientific or abstract principles, precluding, for instance, a patent on the very concept of “hedging.” Finally, Prometheus contends that its patents do not cover natural phenomena at all, since thiopurine drugs, their metabolites, and the process of testing blood are wholly synthetic.


Incentives for Research and Development

At issue in this case are two patents belonging to Respondent Prometheus Laboratories, which concern a correlation between patient metabolite levels and recommended dosages of the immunosuppressive drug thiopurine. Petitioner Mayo Collaborative Services asserts that upholding the validity of these patents may severely impede research and development efforts in the medical industry. According to Mayo, because the patents concern basic natural correlations, Prometheus’s ability to monopolize the correlations may discourage others from investing in innovation and new research. In Mayo’s view, enforcing the patents may enable Prometheus to “bully” potential competitors through litigation, thus deterring market entry and increasing the transaction cost for potential competitors.

Mayo contends that invalidating the patents is unlikely to harm research and innovation incentives, as the development costs for diagnostic tests are low, and studying natural correlations does not involve the heightened risks associated with testing and developing new medical technology. Mayo also argues that the patent process is not the only way for incentivizing research and obtaining necessary funding. For instance, Mayo notes that the government may provide researchers with substantial funding, and that, in any event, research is often driven not by the promise of future revenue, but by researchers’ innate curiosity and desire to improve patient care.

In response, however, Prometheus argues that striking down the patents at issue would erode the entire medical industry’s incentives for future research, discouraging both researchers and their financial sources from pursuing and funding innovative endeavors. Prometheus asserts that strong incentives for innovation are especially important in new fields, such as “personalized medicine,” which require substantial investments in research and in developing and distributing products that help patients. Furthermore, in support of Prometheus, the American Intellectual Property Law Association avers that, without strong patent protection, capital investments in future research and development will decline, and less critical research will be conducted.

Additionally, Prometheus questions Mayo’s contention that the government may be able to make up for lost revenue resulting from invalidated patents. Even if the government could provide the same amount of funding for research, Prometheus argues that the medical industry would still suffer from inefficiency, as the government—a large and complex bureaucracy—is less able than private investors to identify and target promising and valuable research projects. Finally, Prometheus calls into doubt Mayo’s belief that scientists would continue to conduct research solely out of a sense of duty or professional curiosity, without any promise of patent protection.

Impact on the Cost and Quality of Patient Care

Mayo maintains that enforcing the Prometheus patents will ultimately raise the cost of health care: among other things, the patents will force researchers to formulate wasteful and costly methods of circumventing the patents, to spend valuable time conducting patent searches, and to develop complex licensing agreements with patent holders. In turn, the costs of these patent-avoiding maneuvers may eventually be externalized onto health care consumers. Mayo also argues that the quality of patient care may suffer when Prometheus’s competitors—including Mayo itself—are prevented from developing and marketing more accurate and helpful medical tests. Finally, supported by the American College of Medical Genetics and other amici, Mayo asserts that the Prometheus patents and their kind may compromise physicians’ ethical obligation to exercise their best medical judgment, forcing physicians to divert resources away from actual care and to instead choose treatment methods that are less effective, but not patented.

In contrast, Prometheus argues that the medical field and the quality of patient care will be best served by a consistent and predictable process for patent validation. Mayo’s proposal—which, according to Prometheus and its amici, would allow judges to arbitrarily invalidate patents that may adversely affect inventors, the government, or the public—will impose significant costs on the patent system, make patent validation less predictable, and ultimately decrease the quality of innovations in the medical field. Prometheus also challenges Mayo’s assertion that enforcing its patents will place physicians in ethical dilemmas, noting that Mayo holds similar patents but has never raised such ethical concerns.


The outcome of this case may affect the financial incentives for medical research and development in the patent industry, and may also impact the cost and quality of patient health care. Mayo argues that the patents-in-suit cover a natural correlation between thiopurine metabolites and patient health which involves mere data-gathering steps that have long existed in the medical community. Mayo also asserts that the patents would preempt all other useful applications of that correlation. Prometheus, however, contends that the patents cover not the natural correlation itself, but concrete applications of scientific principles in a particular process. Prometheus argues that its patents ultimately improve patient health by indicating how to adjust thiopurine doses for individual patients.

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