EGFR and lung cancer: As compared to deletion mutation, high phosphorylation is detected on tyrosine residues encoded by the codon 845 in the L858 mutation at EGFR exon 21 [18], which may be responsible for the higher response to EGFR-TKIs in lung cancer patients harboring EGFR exon 19 mutation compared to those harboring exon 21 mutation.