Afatinib is an oral irreversible ErbB family blocker that targets epidermal growth factor receptor (EGFR/ErbB1), human epidermal growth factor receptor 2 (HER2/ErbB2), and HER4 (ErbB4) and is approved for the first-line treatment of advanced non–small cell lung cancer (NSCLC) with certain sensitizing EGFR mutations. The gene discussed is EGFR; the disease is lung cancer.