Non-Small Cell Lung Cancer (NSCLC) patients harboring EGFR activating mutations, such as in-frame deletions in exon 19 (Ex19del) or missense mutation in exon 21(L858R), show high sensitivity to EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib, erlotinib, afatinib and dacomitinib. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.