PDCD1 and neoplasm: Activation of the PD-1/PD-L1 pathway inhibits T cell activation, promotes apoptosis of tumor-infiltrating lymphocytes, decreases secretion of inflammatory cytokines, and enhances secretion of the immune inhibitory cytokine interleukin-10 (IL-10), eventually resulting in the escape of tumor cells from immune surveillance (19, 20) (Figure 1).