Several factors secreted by tumor cells stimulate osteoclast activity and bone resorption and among them, PTH was the first to be recognized as involved in malignant osteolysis: in breast cancer cells, treatment with the antibody anti-PTH reduced the development of osteolytic lesions [32] by regulating the RANKL/RANK axis. This evidence concerns the gene TNFSF11 and breast carcinoma.