Sundaresan et al. [45] demonstrated that the use of ctDNA, complemented by mutation analyses of CTCs and tumor biopsies can improve the detection rate of T790M EGFR resistant mutation to molecular targeted therapy of non-small cell lung cancers, first- and second-generation EGFR tyrosine kinase inhibitors. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.