PDCD1 and cancer: Different immunotherapy approaches are currently under development aiming to improve outcomes for cancer patients, such as immune checkpoint inhibitors [CTLA4 and PD-1/PD-L1 axis (2–5)], monospecific (6) and bispecific (7) monoclonal antibodies, immune-stimulatory agents such as BCG (8), cancer vaccines (9), and the adoptive transfer of tumor-reactive immune cells (10).