EGFR and non-small cell lung carcinoma: The single point mutation leucine-858 to arginine (L858R) in exon 21 and variable deletions of at least three amino acid residues in exon 19 are together often referred to as ‘classical’ EGFR activating mutations and represent the vast majority (85–90%) of all observed EGFR kinase domain mutations in NSCLC.18 It is now clear, however, that not all activating EGFR mutations are inherently sensitive to EGFR inhibitors.