CD274 and cancer: The immune system and Treg up-regulation are inhibited when PD-1 binds to PD-L1/PD-L2 in the tumor microenvironment; hence, the immune surveillance system cannot fully play its role in eliminating malignant tumor cells.[14] Immune evasion occurs when tumor cells overexpress PD-L1.[15,16] ICIs repress the binding of PD-1 as well as PD-L1, and reactivate cytotoxic T cells to kill cancer cells.[17] However, the immune balance is disrupted when the immune system is activated, and normal tissues are over-attacked.