The discovery of genetic mutation on tyrosine kinase, such as EGFR mutations including exon 19 deletion (Del19) and exon 21 Leu858Arg substitution (L858R), that confer sensitivity to EGFR-targeted tyrosine kinase inhibitors in lung adenocarcinomas heralded the beginning of the era of precision medicine for lung cancer [91,92]. The gene discussed is EGFR; the disease is lung adenocarcinoma.