DKK1 and cancer: With increasing appreciation for findings that dysregulated Wnt/β-catenin signaling is involved in the development and pathogenesis of many disease types including cancers and autoimmune disorders, such as the SLE [16, 46, 47], several key molecules in Wnt/β-catenin signaling cascade have been investigated as biomarkers for disease diagnosis and/or prognosis [48–53], among them Wnt signaling inhibitor DKK-1 has spurred an increased interest in both cancers and autoimmune diseases [24, 27, 30, 34, 37, 40, 54–56].