Epidermal Growth Factor Receptor (EGFR) is the most common altered targetable gene in NSCLC, and its mutations (mainly exon 19 deletions and exon 21 L8585R mutations) represent the predictive biomarker for first-, second- and third-generation EGFR-Tyrosine Kinase Inhibitors (TKIs). The gene discussed is EGFR; the disease is non-small cell lung carcinoma.