Programmed death-ligand 1 (PD-L1), the ligand of PD-1, belongs to the B7 protein series and is usually expressed on some macrophages and dendritic cells, and tumor cells tend to overexpress PD-L1 in order to escape from immune killing (Ohaegbulam et al., 2015). The gene discussed is PDCD1; the disease is neoplasm.