SFRP1 and breast carcinoma: Consistent with this notion, expression of the extracellular inhibitor of Wnt/β-catenin signaling, secreted frizzled-related protein 1 (also known as SFRP1), which competes with the Wnt signaling receptor FZD for ligand binding, is significantly down-regulated in many breast cancers and is associated with poor survival and a poor therapeutic response15, 16, 17.