DKK1 and cancer: Although the molecular mechanism underlying DKK1-dependent cancer progression was unclear for a long time, it has been recently demonstrated that cytoskeleton-associated protein 4 (CKAP4) is a receptor for DKK1 and that DKK1 activates the phosphoinositide 3-kinase (PI3K)-AKT pathway by binding CKAP4, thereby stimulating cancer cell proliferation [9, 11, 21].