MDK and liver cancer: To explore whether FNDC4 could act as a biomarker in HCC, we studied the correlation between the expression of FNDC4 and AFP, a primary hepatocellular carcinoma-specific tumor marker, and other liver cancer-related genes, such as Glypican 3 (GPC3), Midkine (MDK) and Dickkopf WNT signaling pathway inhibitor 1 (DKK1).