Two mutations, the deletions that were discovered in exon 19, which affect the conserved Long-range epigenetically active (LREA) domain motif, and the single amino acid substitution L858R through exon 21 at codon 858 (Leucine to Arginine; L858R), are referred to as "classical" EGFR mutations since they account for 85 percent of identified gene mutations in NSCLC and confer responsiveness to EGFR kinase inhibitors (EGFRi) [15]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.