PDCD1 and lung cancer: Additionally, the regulatory approval of monoclonal antibodies (mAbs) blocking the immune checkpoints, namely, the programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) pathway and the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), known as immune checkpoint inhibitors (ICPi), has altered the survival rates of lung cancer [13,20].