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Are Medical Diagnostic Methods Patent Ineligible by Convention?: CareDx, Inc. v. Natera, Inc. and Eurofins Viracor, Inc.
Tuesday, January 31, 2023

In CareDx, Inc. v. Natera, Inc., the U.S. Court of Appeals for the Federal Circuit held that CareDx’s patent claims to methods of detecting organ transplant rejection were invalid as patent ineligible under 35 U.S.C. § 101.1 Affirming the district court, the Federal Circuit determined that CareDx’s claims “are directed to a natural law together with conventional steps to detect or quantify the manifestation of that law,”2 relying on “admissions” in the patents themselves that the claims recited only “conventional” techniques.’


In the medical diagnostics field, patent subject matter eligibility under 35 U.S.C. § 101 has been the subject of numerous cases in the years following the Supreme Court decisions in Mayo Collaborative Services v. Prometheus Laboratories, Inc.3 and Alice Corp. v. CLS Bank Int’l.4 Following Mayo and Alice, courts apply a two-step test to determine whether a patent claim is directed to ineligible subject matter. Step 1 is to determine whether the claims are directed to a law of nature or natural phenomenon. If so, Step 2 is to determine whether the other limitations of the claim transform the claim into a patent-eligible application of the natural phenomenon; merely adding “conventional” steps to a natural phenomenon do not make the claim patentable.’

Here, Stanford is the owner of U.S. Patent Nos. 8,703,652, 9,845,497, and 10,329,607 (“the subject patents”), all of which are titled “Non-Invasive Diagnosis of Graft Rejection in Organ Transplant Patients” and share the same specification. The claimed diagnostic methods involve detecting a donor’s cell-free DNA (“cfDNA”). “When an organ transplant is rejected, the recipient’s body, through its natural immune response, destroys the donor cells, thus releasing cfDNA from the donated organ’s dying cells into the blood. These increased levels of donor cfDNA—which occur naturally as the organ’s condition deteriorates—can be detected and then used to diagnose the likelihood of an organ transplant rejection.”5 Stanford licensed the subject patents to CareDx, Inc.

District Court Granted Summary Judgment

CareDx sued Natera, Inc. (“Natera”) and Eurofins Viracor, Inc. (“Eurofins”) for infringing the subject patents.6 CareDx asserted method claims with the following steps:

  1. “Obtaining” a sample from the recipient that contains cfDNA;

  2. “Genotyping” the transplant donor and/or recipient to develop polymorphism or SNP profiles;

  3. “Sequencing” the cfDNA from the sample using multiplex or high-throughput sequencing; or performing digital PCR; and

  4. “Determining” the amount of donor cfDNA in the sample.7

    The district court granted summary judgment of invalidity under 35 U.S.C. § 101 in favor of Natera and Eurofins. The district court held that CareDx’s “asserted claims were directed to the detection of natural phenomena, specifically, the presence of donor cfDNA in a transplant recipient and the correlation between donor cfDNA and transplant rejection.” Importantly for the Mayo Step 2 analysis, the district court pointed to “the specification’s numerous admissions,” that “the claims recited only conventional techniques.”8

    Federal Circuit Affirmed

    On appeal, CareDx argued that “the claimed advance is improved measurement methods” and “that the district court did not properly perform the step one analysis because it concluded that step one is essentially the same as step two and centers on conventionality.”9 But the Federal Circuit affirmed the summary judgement, holding the asserted claims are ineligible under § 101. The Federal Circuit agreed that the claims are directed to a natural law and employed “conventional steps to detect or quantify the manifestation of that law.”10

    Under Alice/Mayo Step 1, the Federal Circuit explained that “[t]his is not a case involving a method of preparation or a new measurement technique.”11 The techniques referred to in the claimed methods are “conventional measurement techniques to detect a natural phenomenon‒the level of donor cfDNA and the likelihood of organ transplant rejection.”12 It also clarified that the conventionality inquiry is not limited to Alice/Mayo Step 2. “On the contrary, and as the district court recognized, we have repeatedly analyzed conventionality at step one as well.”13 The Federal Circuit further explained “that the two stages involve overlapping scrutiny,” and “there can be close questions about when the inquiry should proceed from the first stage to the second.”14

    Under Alice/Mayo Step 2, the Federal Circuit held that “CareDx’s asserted claims add nothing inventive at step two because they only recite detection methods that simply append conventional steps, specified at a high level of generality to natural phenomena.”15 The Federal Circuit agreed with the district court that each of the methods in the recited steps were already being performed by those in the art, and the claimed combination of steps added nothing inventive.16

    Looking Forward

    Claims to medical diagnostics face unique challenges. When they employ conventional techniques, courts continue to hold them invalid under § 101. In spite of that trend, there are still ways to claim medical diagnostic inventions following Mayo. For example, in Illumina, Inc. v. Ariosa Diagnostics, Inc., the Federal Circuit held a method of sample preparation to be patent eligible under step 1 of Mayo—“conclud[ing] that the claims [we]re not directed to [a] natural phenomenon but rather to a patent-eligible method that utilize[d] it.”17

    The lesson from CareDx for those prosecuting patents is to avoid describing techniques used in the claimed invention as “conventional,” even if such statements support enablement of the claims. Moreover, instead of claiming methods of detecting, applicants should consider claim forms like methods of sample preparation, such as the claims at issue in Illumina. We note that the Stanford patents at issue in CareDx were filed before the Mayo decision. Going forward, others may be able to avoid that misfortune.


    1. CareDx, Inc. v. Natera, Inc., 40 F.4th 1371, 1381 (Fed. Cir. 2022), rehearing denied at ECF No. 75 (Dec. 2, 2022).

    2. Id.

    3. 566 U.S. 66 (2012).

    4. 573 U.S. 208 (2014).

    5. CareDx, 40 F.4th at 1372‒1373.

    6. Id.

    7. Id. at 1375.

    8. Id. at 1375‒1376 (emphasis added).

    9. Id.

    10. Id. at 1381.

    11. Id.

    12. Id. at 1378 (emphasis added).

    13. CareDx, 40 F.4th at 1379 (citing Athena Diagnostics, Inc. v. Mayo Collaborative Servs., LLC, 915 F.3d 743, 751 (Fed. Cir. 2019); Cleveland Clinic Found. v. True Health Diagnostics LLC, 859 F.3d 1352, 1361 (Fed. Cir. 2017)) (quotations omitted).

    14. CareDx, 40 F.4th at 1379 (citing Elec. Power Grp., LLC v. Alstom S.A., 830 F.3d 1350, 1353 (Fed. Cir. 2016)).

    15. CareDx, 40 F.4th at 1380 (citing Mayo, 566 U.S. at 82) (internal quotations omitted).

    16. CareDx, 40 F.4th at 1380.

    17. 952 F.3d 1367, 1372, 1374 (Fed. Cir. 2020) (emphasis in original).

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