EGFR and lung adenocarcinoma: Uncommon EGFR mutations such as exon 18 (E709X and G719X), exon 19 (exon 19 insertions), exon 20 (exon 20 insertions and S768I), and exon 21 (L861Q) mutations constitute the remaining 10–15% of EGFR-mutated lung adenocarcinomas, which display variable sensitivities to EGFR TKIs [17].