EGFR and lung adenocarcinoma: EGFR exon 19 deletion (del19) and exon 21 Leu858Arg substitution (L858R) make up around 90% of all EGFR mutation-positive lung adenocarcinomas, and are strongly associated with robust responses and improved progression-free survival (PFS) to EGFR tyrosine kinase inhibitors (EGFR-TKIs) [3].