EGFR and non-small cell lung carcinoma: Although classical drug-sensitizing mutations account for 80% to 90% of EGFR mutations observed in NSCLC [L858R point mutation and exon 19 deletions (E19del)], 10% to 20% of patients with EGFR-mutant NSCLC present with atypical mutations, most notably exon 20 insertions (E20ins; refs. 25, 26).