For instance, the gatekeeper mutation substituting threonine for methionine at amino acid position 790 (T790M) in exon 20 of EGFR confers resistance to first- and second-generation EGFR-TKIs in 50–60% of EGFR-mutant NSCLC under TKI treatment (Fig. 2) [23, 29, 36]. This evidence concerns the gene EGFR and non-small cell lung carcinoma.