DKK1 and cancer: Dysregulation of the WNT pathway is a common event in a variety of cancers and this can result from the loss of WNT antagonists like SFRP1, its family members SFRP2-5 and the Wnt inhibitory factor 1 (WIF1) gene or by loss of the Dickkoft genes (DKK1-4) that bind the low-density lipoprotein receptor-related protein 5/6 component of the WNT receptor complex (Figure S7 in File S1) [42].