PDCD1 and cancer: Among various immunotherapeutic strategies, the immune checkpoint blockade (ICB) has the broadest impact and prospects, with several antibodies targeting CTLA4 (cytotoxic T lymphocyte antigen 4), PD1 (programmed cell death 1), and PD-L1 (PD-1 ligand 1) approved by the FDA for the treatment of a number of different cancers [3,4,5].