PDCD1 and cancer: For T cells, PD-1/PD-L1 ligation inhibits TCR proximal signaling molecules phosphorylation, PI3K–Akt–mTOR pathway and Ras–MEK–ERK pathway, it also contributes to dysfunction of T cell–dendritic cell interaction and metabolic alteration; for cancer cells, PD-L1 leads to antiapoptotic effect, immune evasion, PI3K–Akt–mTOR pathway activation and glycolysis, which facilitate cancer cell survival (Figure 1) (58).