Currently, four companion diagnostics have FDA approval for ctDNA testing: The Cobas EGFR Mutation Test v2 (Heeke et al., 2020) (nonsmall cell lung cancer); Therascreen® PIK3CA RGQ test (Andre et al., 2019) (breast cancer); Guardant360 CDx test (Guardant360) (EGFR mutations); and FoundationOne Liquid CDx (FoundationOne) (prostate and nonsmall cell lung cancer). Here, EGFR is linked to breast cancer.