PDCD1 and cancer: Particularly, the programmed death receptor-ligand 1 (PD-L1) plays a crucial role in the metastatic spread of tumors by binding to programmed death receptor 1 (PD-1) on CD8+ T cells, thus imparting a potent immune evasive character to cancer cells mainly by altering effector functions of T cells, along with the inhibition of T cell proliferation and survival [10,11].