Background
CareDx, Inc. licensed three Stanford University patents covering methods for non-invasively detecting organ transplant rejection. When a transplanted organ is being rejected, the recipient’s immune system destroys donor cells, which release the donor’s cell-free DNA (cfDNA) into the recipient’s bloodstream. Elevated levels of donor cfDNA signal that rejection may be occurring. The Stanford patents claimed methods of detecting this donor cfDNA in a blood sample and using the detection to diagnose or predict rejection status.
Natera, which operates a competing liquid biopsy diagnostic service, was sued for infringement. The District of Delaware granted summary judgment that the asserted claims were ineligible under § 101. CareDx appealed to the Federal Circuit.
The Court’s Holding
The Federal Circuit affirmed. Applying the Mayo/Alice framework, the court held the claims were directed to a natural phenomenon — the naturally occurring increase in donor cfDNA in a recipient’s bloodstream during organ rejection. At step two, the court found that the specific laboratory techniques used in the claims (collecting blood, genotyping, sequencing, and quantifying cfDNA) were conventional, well-understood methods borrowed from other diagnostic contexts such as cancer detection and prenatal testing. The patents’ own specifications acknowledged that these techniques were conventional — a damaging admission the court relied on heavily.
The court rejected CareDx’s argument that combining these conventional techniques in a new application constituted an inventive concept, holding that applying conventional techniques to a newly discovered natural phenomenon does not automatically render the combination patent eligible. CareDx’s petition for en banc rehearing was denied, and the Supreme Court later declined certiorari.
Key Takeaways
- Diagnostic methods based on detecting naturally occurring phenomena in body fluids remain at high risk of invalidation under § 101, even when the natural phenomenon was newly discovered.
- Patent specifications that describe the claimed laboratory techniques as “conventional” or “standard” provide ammunition for § 101 challenges at step two.
- Combining known techniques in a new diagnostic context does not create an inventive concept sufficient to save claims directed to a natural phenomenon.
- The continued stream of diagnostic patent invalidity decisions — from Athena to CareDx — reflects the unresolved tension between Mayo and Congress’s intent to protect medical innovations.
Why It Matters
CareDx v. Natera is one of the most significant post-Athena diagnostic patent decisions, underscoring that the Federal Circuit has consistently applied Mayo to invalidate medical diagnostic claims based on natural biological phenomena. The case is particularly striking because the underlying science — liquid biopsy-based transplant monitoring — represents a genuine advance in patient care that reduces the need for invasive tissue biopsies to monitor transplanted organs.
The decision illustrates the policy tension at the heart of the diagnostic patent eligibility debate: the same legal framework that prevents monopolization of natural laws also removes financial incentives for companies to invest in developing, validating, and commercializing novel diagnostic tests. This paradox continues to drive legislative proposals to reform § 101, with diagnostic patents frequently cited as the primary casualty of the current regime.