In the present study, we first confirmed the DKK-1 protein expression in both MM cell lines and primary myeloma cells, and subsequently identified much lower β-catenin mRNA expression in SCs from patients with MM compared with those in primary myeloma cells and normal SCs, indicating the inhibition of Wnt signaling in patients' SCs in contrast to its activation in myeloma cells. The gene discussed is DKK1; the disease is plasma cell myeloma.