PDCD1 and neoplasm: Recently, researchers have identified some important immune checkpoint components that promote the tumor cells to evade from the immune surveillance, such as cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1)/programmed cells Death ligand 1 (PD-L1) (Brunner-Weinzierl and Rudd, 2018; Lee et al., 2019).