Bisphosphonates in oncology: evidence for the prevention of skeletal events in patients with bone metastases

Bone metastases frequently occur in patients with advanced solid tumors, particularly breast and prostate cancers, and nearly all patients with multiple myeloma have some degree of skeletal involvement. The strides made in treating these primary tumors have extended median survival times and thereby increased patient risk for skeletal-related events (SREs), including pathologic fractures, spinal cord compression, need for palliative radiation therapy or surgery to bone, and hypercalcemia. Bisphosphonates, inhibitors of osteoclastic bone resorption that were first established as treatment of osteoporosis, have been shown to prevent and/or delay SREs related to malignancy. The results of a large, randomized phase 3 study comparing zoledronic acid and pamidronate in breast cancer or multiple myeloma patients with osteolytic lesions showed that the incidence of SREs, time to first SRE, and risk of developing a SRE were similar between treatment groups. However, in patients with solid tumors (excluding breast or prostate cancer) metastatic to the bone, only zoledronic acid has demonstrated clinical efficacy. Although bone turnover marker levels, such as N-telopeptide of type I collagen, have been shown to correlate with clinical response, additional studies are needed to validate their ability to predict response to bisphosphonate therapy.