Although previous studies have focused on the association between plasma EGFR mutation copy numbers and the efficacy of osimertinib at pretreatment, Sakai et al.18 evaluated the clinical significance of monitoring the ctDNA of EGFR-TKI-sensitizing mutations and EGFR T790M mutation in EGFR T790M-positive patients with NSCLC at pretreatment, on day 1 of treatment cycle 4 or 9, and at the diagnosis of PD using digital PCR. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.