EGFR and neoplasm: Background: Among patients with non-small cell lung cancer (NSCLC), we compared the progression-free survival (PFS) and proportion of acquisition of T790M mutation of the epidermal growth receptor gene (EGFR) after first-line treatment with epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) in patient groups with and without tumor expression of programmed death ligand-1 (PD-L1).