CD274 and neoplasm: The PD-1 pathway, which includes the immune cell co-receptor programmed death 1 (PD-1) and its ligands, programmed cell death ligand 1 (PD-L1) and programmed cell death ligand 2 (PD-L2), acts on local immunosuppression in the tumor microenvironment (TME) [41,42,43].