This problem of low or undetectable variant AFs in cfDNA is illustrated by the fact that, in our study, for four patients with a known EGFR or KRAS mutation in the tissue biopsy, only one variant was detectable in cfDNA by using CAPP-sequencing, and that for 17 patients in whom no cfDNA variant was detected, one to nine (in total 48) tissue variants were detected by using Roche’s AVENIO Tumor Tissue Surveillance assay. The gene discussed is EGFR; the disease is neoplasm.