PTK2 and hepatocellular carcinoma: SFRP1, a secreted Wnt antagonist, and SCARA5, a plasma membrane protein, which activate the focal adhesion kinase (FAK) signaling pathway and inhibit the tyrosine phosphorylation cascade of the FAK-Src-Cas pathway, are strong candidate tumor suppressor genes due to their antiproliferative effect on HCC cells (39,41).