PDCD1 and cancer: Immune check-point blockade has shown unprecedented superiority to prior therapies in cancer treatment as demonstrated by significantly prolonged survival of patients given anti-cytotoxic T lymphocyte-associated antigen-4 (anti-CTLA-4, Ipilumimab) [1], anti-programmed death-1 (anti-PD-1, Pembrolizumab and Nivolumab) [2, 3], or anti-PD-L1 (anti-PD-Ligand 1, Atezolizumab) [4] antibodies.