Interaction between bone cells and bone marrow microenvironment cells in promoting both malignant plasma cell survival and bone lesions in MM patients. Myeloma cells can directly support osteoclast formation and activity as well as inhibit osteoblast differentiation by releasing numerous cytokines. Moreover, other molecules can be secreted by bone cells and other cells interacting with each other in the bone microenvironment, thus supporting both the progression of MM tumor burden and the development of MM bone disease.