It has been previously demonstrated that the 5TMM murine multiple myeloma cells express RANKL. RANKL is known to interact with RANK on osteoclasts, cells responsible for the degradation of bone. In the present work, how this RANK/RANKL interaction is involved in the development of multiple myeloma is being investigated. An in vivo murine model of multiple myeloma will be used to analyze how the expression of this molecule and its receptor is regulated and whether blocking this interaction in vivo has any beneficial effect on the tumor development and associated osteolytic lesions.