PD-1 is a type I transmembrane protein receptor expressed on the surface of numerous immune cells such as macrophages, dendritic cells, T-cells, B-cells, and natural killer cells.[7,9] PD-L1 and PD-L2 both act on PD-1.[10,11] However, the main function of T-cell regulation within the tumor microenvironment depends on PD-L1, which is expressed on the same cells that express PD-1. The gene discussed is PDCD1; the disease is neoplasm.