GDF15 and hepatocellular carcinoma: The other 6 proteins tested were chosen because of their reported involvement in liver diseases (e.g. GDF15, which has been shown to be involved in liver disease and hepatocellular carcinoma [38]) and other cancers (as is the case for CEA, IGFBP2, B2M, PDGF-Rb and OPN [39–42]).