DCN and plasma cell myeloma: The direct effect of osteoblasts was reported to induce apoptosis and cause cell cycle arrest of myeloma cells, when cultured with osteoblasts induced from the MC3T3-E1 cell line or with primary bone marrow stromal cells.232 In particular, Decorin has been identified as a key factor produced by osteoblasts that inhibits the proliferation and survival of myeloma cells through activation of p21233 (Fig. 6.3).