DKK1 and plasma cell myeloma: Myeloma cells secrete Dickkopf-related protein 1 (DKK-1), IL-3, HGF and TGF-β to inhibit osteoblasts, and they secrete RANKL, TNF, lymphotoxins, SDF-1 and MIP-1α to activate osteoclasts.This inhibition of osteoblasts and activation of osteoclasts results in increased levels of bone-derived tumor growth factors that further promote the expansion and proliferation of myeloma cells [78].