TNFRSF11B and plasma cell myeloma: The proteoglycan Syndecan-1 (CD138), the hallmark of normal and malignant plasma cells, is covered with covalently bound heparan and chondroitin sulfate side chains [14] allowing it to act as most important “sponge” for heparan sulfate binding myeloma growth and survival factors such as VEGF or IGF-1, as well as factors impacting in bone turnover, e.g. osteoprotegerin (OPG), a decoy receptor for receptor activator of NFκB ligand thus preventing the OPG-mediated inhibition of osteoclastic bone resorption [52].