MDK and hepatocellular carcinoma: Recent studies have identified a number of biomarkers in the early detection of HCC, including alpha-fetoprotein (AFP) [9–11], lens culinaris agglutinin-reactive alpha-fetoprotein (AFP-L3) [10,12–13], des-gamma-carboxyprothrombin (DCP) [9–10, 13], glypican-3 (GPC-3) [14–15], cytokeratin 19 (CK19) [15], golgi protein 73 (GP73) [16], microRNA (miRNA) [17–18], osteopontin (OPN) [11,19], annexin A2 [20] and midkine (MDK) [21].