In addition to DKK-1, there is evidence that myeloma cells also secrete another soluble Wnt inhibitor, frizzled-related protein-2 (FRP-2), that may play a role in dysregulation of osteoblast differentiation.(49) Secretion of soluble FRP-2 (sFRP-2) was often found in patients having advanced bone lesions. Here, DKK1 is linked to plasma cell myeloma.