OCs, in turn, also release several soluble factors (including IL6, CCL3, OPN, B-cell activating factor (BAFF), and a-proliferation-inducing ligand (APRIL)), which promote MM cell growth and survival, thus creating a vicious cycle between bone lesions and myeloma progression (see reviews [126,179]). Here, TNFSF13 is linked to plasma cell myeloma.