Optimizing bisphosphonate therapy in patients with breast cancer on endocrine therapy

Deterioration of bone health is a major concern during progression and treatment of patients with breast cancer, especially in postmenopausal women. Disease- and treatment-associated skeletal-related events include fractures, spinal compression, bone pain, and hypercalcemia of malignancy. Bisphosphonates, which inhibit osteoclastic bone resorption, are important new agents in the management of skeletal-related events, and their impact on breast cancer-related bone metastases and on bone loss during long-term estrogen deprivation therapies such as aromatase inhibitors is reviewed. Intravenous pamidronate has become the standard bisphosphonate to reduce or delay skeletal complications of advanced breast cancer bone metastases, but the more potent agent, zoledronic acid, appears to be at least as effective. Another agent, ibandronate, is also active but has not been investigated in comparison with the other intravenous bisphosphonates. Zoledronic acid is the most convenient to administer, requiring only a short infusion. The effects of bisphosphonates on bone health in women with early breast cancer are also being investigated. A single yearly infusion of zoledronic acid has been shown to significantly increase bone mineral density in osteoporotic postmenopausal women and to reduce biochemical markers of bone turnover. The possibility of such treatment-reversing aromatase inhibitor-associated bone loss during adjuvant therapy of breast cancer is being evaluated in a trial of letrozole, with zoledronic acid added initially or after the onset of bone loss or fracture.