Compared with the control bone tissues and the bone biopsies obtained from patients with nonmetastatic primary tumors (i.e., breast carcinoma, lung adenocarcinoma, and prostate carcinoma), patients with bone metastatic lesions from the 3 aforementioned primary tumors, as well as osteolytic lesions obtained from the bone biopsies of patients with multiple myeloma, demonstrated diminished expression of osteoprotegerin, which is a negative regulator of osteoclastogenesis. The gene discussed is TNFRSF11B; the disease is breast carcinoma.