Osimertinib is the third-generation, pyrimidine-based, irreversible epidermal growth factor receptor-tyrosine kinase inhibitor that received approval from the FDA in November 2015 and has become the standard approach in patients with advanced, epidermal growth factor receptor (EGFR) mutated non-small cell lung cancer (NSCLC), especially with brain metastases. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.