During osteolytic bone metastasis, tumor cells continuously secrete a variety of osteoclastogenic cytokines in the bone, including CSF-1, PTHrP, RANKL, IL-8, IL-11, prostaglandin E, matrix metalloproteinase 1 (MMP-1), stromal cell communication network (CCN), and TNF-α (150–156). The gene discussed is CSF1; the disease is neoplasm.