SFRP2 and plasma cell myeloma: Secondly, myeloma cells secrete factors that inhibit differentiation of osteoblasts, such as Dickkopf 1 (DKK-1), tumour necrosis factor alpha (TNF-α), soluble frizzled-related protein-2 (SFRP-2), and Activin A. DKK-1 and SFRP-2 act by inhibiting the Wnt pathway, a pathway that plays a significant role in osteoblastic maturation [9].