EGFR exon 20 insertion mutations are heterogeneous at the molecular level but can be characterized as inframe insertions or duplications of between 3 and 21 bp (corresponding to 1 to 7 amino acids) clustered between amino acid positions 762 and 774 of the EGFR protein.22 The most common insertion sites in EGFR in NSCLC are shown in Fig. 2. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.