EGFR and cancer: Both pseudo-positive (cfDNA positive, re-biopsy tissue negative) and pseudo-negative (cfDNA negative, re-biopsy tissue positive) were observed, which were considered to result from biological features of cfDNA, such as the tumor heterogeneity of each cancer nodule that is considered to have greater impact in case of acquired resistance mutation for EGFR-TKI treatment [19], influence of drug treatment on cfDNA shedding in tumor sites and tumor size.