CD274 and neoplasm: The PD-1 axis has been recognized as a pivotal immune checkpoint and the interaction between PD-1 and its ligand PD-L1 inhibits T-lymphocyte proliferation, survival, and effector functions (such as cytotoxicity and cytokine release) [71], induces apoptosis of tumour-specific T-cells [72], as well as resistance of tumour cells to cytolytic T-lymphocyte attack [73,74].