For example, in EGFR-mutant lung cancers, the point mutation leading to a substitution of methionine for threonine at amino acid position 790 in exon 20 of EGFR, known as the EGFR T790M gatekeeper mutation, is a leading cause of resistance to first- and second-generation EGFR inhibitors [11,12]. The gene discussed is EGFR; the disease is lung carcinoma.