PDCD1 and cancer: Blockade of immune checkpoints, such as cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death-1 (PD-1)/ programmed cell death ligand-1 (PD-L1) signaling, have demonstrated broad anti-cancer activities with an acceptable side effect profile in different cancer types, including NSCLC [5–9].