PD-L1 was up-regulated after the development of acquired resistance to gefitinib in epidermal growth factor receptor-mutant non-small cell lung cancer (NSCLC), involving the epithelial-mesenchymal transition (EMT) and MAPK/ERK kinase (MEK) pathway [13, 14]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.