PDCD1 and lung adenocarcinoma: Lung adenocarcinoma (LUAD) is one of the most benefitted cancers in the era of cancer immunotherapy according to several landmark clinical trials supporting the use of immune checkpoint blockades (ICB), anti-programmed cell death 1 (PD-1) antibody and anti-programmed cell death ligand 1 (PD-L1) antibody 1-3.