We previously established the mutation-biased PCR and quenching probe (MBP-QP) method to detect T790M and succeeded in detecting T790M in ctDNA with detection rates of 53% and 40%, respectively, among lung cancer patients who acquired resistance to EGFR-TKI in a retrospective study [23] and a multi-centered prospective study [24]. The gene discussed is EGFR; the disease is lung carcinoma.