Current status and future directions in the treatment of bone metastases from breast cancer.

The clinical treatment of bone metastasis from breast cancer is currently based on the systemic administration of antiresorptive agents, radiopharmaceuticals, and/or local treatments such as radiation therapy, radiofrequency ablation and surgery. However, these therapeutic options are merely palliative and do not show to have a significant positive impact on patients' survival. In addition, the systemic administration of antiresorptive drugs and/or antitumour agents and/or radiopharmaceuticals may negatively affect normal bone metabolism with detrimental consequences for cancer patients. Hence, the need to identify alternative therapeutic strategies that, based on the hallmarks of bone metastasis, can effectively thwart tumour cell growth while, at the same time, overcoming antitumour drug-induced bone loss and preserving bone health. To this aim, current studies are directed toward the development of new molecules with low toxicity and/or novel drug delivery systems, which may efficiently hinder the growth of metastatic cells, while other studies are focussed on the design of new clinical treatments that, by acting on early stages of breast cancer, may prevent the homing and the subsequent growth of cancer cells in the bone. These treatments might also target occult micro-metastases before their development into clinically evident bone lesions, ultimately hindering bone relapse and disease progression. However, this therapeutic approach implies the identification of early stage breast cancer patients being at high risk of developing bone metastases. The discovery of novel specific biomarkers as predictor of metastatic bone disease may help clinicians in selecting these patients.