About 90% of NSCLC-specific sensitizing EGFR mutations are either in-frame microdeletions around the Leu–Arg–Glu–Ala (LREA) residues of exon 19 (known as Del19) or missense leucine-to-arginine substitution at codon 858 (L858R) in exon 21 [26,27]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.