TNF and neoplasm: Tumor cells in turn secrete PTHrP, activated vitamin D, tumor necrosis factor (TNF), matrix metalloproteinases (MMPs), interleukin-6 (IL-6), and other factors, which stimulate the expression of the receptor activator of nuclear factor NF-kB ligand (RANKL) on OBs, leading to the final stimulation of osteoclastogenesis from local OC precursors (3, 20).