Animal studies using mouse models of breast cancer metastasis to bone have demonstrated that administration of recombinant osteoprotegerin (OPG), the RANKL decoy receptor, decreases the number of tumour-associated osteoclasts and reduces levels of bone resorption, thus confirming a role for RANKL in tumour-induced, osteoclast-mediated bone destruction [17,18]. This evidence concerns the gene TNFRSF11B and neoplasm.