## Facts

- Prometheus Laboratories, Inc. held exclusive licenses to two patents claiming methods to optimize thiopurine drug dosing for autoimmune diseases.
- The claims recited: (1) administering a thiopurine drug, (2) determining metabolite levels in the patient’s blood, and (3) “wherein” ranges indicating a need to increase or decrease dosage based on correlations between metabolite concentrations and likely toxicity or ineffectiveness.
- Mayo Collaborative Services used thiopurine metabolite testing in its clinical diagnostic laboratory services, leading Prometheus to assert infringement.
- The district court found infringement but granted summary judgment that the claims were invalid under 35 U.S.C. § 101 as effectively claiming natural correlations.
- The Federal Circuit twice upheld eligibility (including after a Supreme Court vacatur and remand in light of *Bilski*), relying on the machine-or-transformation test.
- The Supreme Court granted certiorari and reviewed whether these diagnostic method claims were patent-eligible subject matter.

## Issues

1. Whether method claims directed to correlations between metabolite levels and drug efficacy/toxicity are impermissibly directed to a law of nature under 35 U.S.C. § 101.
2. Whether adding steps of administering a drug and measuring metabolite levels makes such claims patent-eligible when those steps are routine and conventional.
3. Whether § 101 requires an additional “inventive concept” beyond the natural law, independent of novelty and nonobviousness analyses under §§ 102 and 103.

## Decision

- The Supreme Court unanimously reversed the Federal Circuit.
- The Court held the claims invalid under § 101 because they effectively claimed a law of nature.
- The Court concluded the administering and determining steps were well-understood, routine, conventional activities and did not add enough to transform the natural correlation into a patent-eligible application.
- The Court rejected treating § 101 as satisfied whenever other patentability provisions could address overbreadth or lack of invention, holding that § 101 performs an independent gatekeeping function.

## Legal Principles

- Laws of nature, natural phenomena, and abstract ideas are not patentable under § 101, even when drafted as processes.
- A claim applying a law of nature must include additional elements that amount to “significantly more” than stating the law and directing practitioners to apply it.
- Adding only well-understood, routine, conventional steps—such as standard administration of a drug and conventional measurement techniques—does not supply the required inventive concept.
- The machine-or-transformation test is a relevant clue but not determinative, and cannot override the law-of-nature bar when the claim’s additional steps are conventional.
- § 101 cannot be displaced by §§ 102, 103, or 112; courts must independently assess whether a claim would preempt use of a natural law in practical applications.

## Conclusion

The Court held that claims reciting a natural correlation and instructing doctors to administer a drug, measure metabolite levels, and adjust dosage based on known ranges were not patent-eligible because the added steps were routine and did not limit the claim to a patentable application of the law of nature.


Mayo Collaborative Servs. v. Prometheus Labs., Inc., 566 U.S. 66 (2012)