PDCD1 and cancer: Immune checkpoint blockade (ICB) therapy such as immune-checkpoint proteins programmed cell death 1 (PD-1), programmed cell death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) targets has been reported to provide clinical benefits for cancer immunotherapy in some advanced-cancers such as melanoma and NSCLC [21, 22].