To the Editor The blood-diagnostics field has evolved in the past decade, realizing the ability to detect driver mutations and resistance clones, allowing the application of targeted therapies and the concept of molecular selection and therapeutic monitoring using “liquid biopsy.”1,2 Recently in JAMA Oncology, Torga and Pienta3 reported divergent results between 40 patient-paired blood samples in advanced prostate cancer using 2 commercially available cell-free circulating tumor DNA (ctDNA) tests (Guardant360 and PlasmaSelect). The results indicated low congruence between the 2 tests, and the authors concluded that the data were concerning with regard to standard clinical use of ctDNA.