In previous studies, many special fields have summarized the most-cited studies in their specialty with bibliometric method, such as hepatocellular carcinoma (34), gastric cancer (35), psychosomatic research (36), programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors (37), metabolic disorders (38, 39), and so on. Here, PDCD1 is linked to hepatocellular carcinoma.