PDCD1 and cancer: The expression of programmed death 1 (PD1) / programmed death-ligand 1 (PDL1), cytotoxic T-lymphocyte-associated antigen 4 (CTLA4), and other immune checkpoints, is often significantly increased in malignant tumors and is associated with poor prognosis (Liu et al., 2020a; Ma et al., 2019).