The finding that Dickkopf1 (Dkk1) is a dual function protein demonstrates a mechanism for the coordination of cell migration and antagonism of Wnt/β-catenin signaling during developmental and pathological processes. The profile of Dkk proteins expressed by human breast cancers correlates with indicators of outcome: Dkk1 associates with markers of poor prognosis whereas expression of single function Dkk2 or Dkk3 (which inhibit Wnt/β-catenin signaling and promote migration, respectively) correlates with phenotypes reflective of good prognosis. Therefore, the pro-migratory activities of Dkk1 and 3 identified here offer new insights into breast cancer progression and a potential avenue for therapeutic intervention.