Abbreviations: AFP = alpha-fetoprotein, AUC = area under the curve, CI = confidence interval, CNKI = China National Knowledge Infrastructure, CTCs = circulating tumor cells, ctDNA = circulating tumor DNA, DOR = diagnosis odds ratio, EVs = exosomes, HCC = hepatocellular carcinoma, NLR = Negative likelihood ratio, PLR = positive likelihood ratio, QUADAS-2 = Quality Assessment of Diagnostic Accuracy Studies-2, SROC = summary receiver operating characteristic. The gene discussed is AFP; the disease is hepatocellular carcinoma.