EGFR and non-small cell lung carcinoma: In-frame base pair insertions in exon 20 result in constitutive activation of EGFR, but unlike the more common ‘classical’ activating EGFR mutations (L858R and exon 19 deletions), they have been associated with de novo resistance to targeted EGFR kinase inhibitors [16–18] EGFR exon 20 insertions vary in length (between 3–21 base pairs) and point of insertion (between codons 767 and 774) but when collectively grouped together, this class of mutations are the third most common type of EGFR mutation in NSCLC reported at between 4–10% of all EGFR mutations [17,19–21].