PDCD1 and neoplasm: The programmed cell death protein-1 (PD-1)/programmed cell death protein ligand 1 (PD-L1) interactions between tumor cells and CD8+ T cells were discovered in hepatocellular carcinoma (HCC), where it was found that an increased distribution of CD8+ PD-1+ T cells in tumors predicted poor disease progression and postoperative recurrence [17].