Bisphosphonates as Treatment of Bone Metastases

Accelerated bone loss is a common clinical feature of advanced breast cancer, and anti-resorptive bisphosphonates are the current standard therapy used to reduce the number and frequency of skeletal-related complications experienced by patients. Bisphosphonates are potent inhibitors of bone resorption, acting by inducing osteoclast apoptosis and thereby preventing the development of cancer-induced bone lesions. In clinical use bisphosphonates are mainly considered to be bone-specific agents, but anti-tumour effects have been reported in a number of in vitro and in vivo studies. By combining bisphosphonates with chemotherapy agents, growth and progression of breast cancer bone metastases can be virtually eliminated in model systems. Recent clinical trials have indicated that there may be additional benefits from bisphosphonate treatment, including positive effects on recurrence and survival when added to standard endocrine therapy. Whereas the ability of bisphosphonates to reduce cancer-induced bone disease is well established, their potential direct anti-tumour effect remain controversial. Ongoing clinical trials will establish whether bisphosphonates can inhibit the development of bone metastases in high-risk breast cancer patients. This review summarizes the main studies that have investigated the effects of bisphosphonates, alone and in combination with other anti-cancer agents, using in vivo model systems of breast cancer bone metastases. We also give an overview of the use of bisphosphonates in the treatment of breast cancer, including examples of key clinical trials. The potential side effects and future clinical applications of bisphosphonates will be outlined.