The role of bisphosphonates in breast cancer

Breast cancer frequently metastasizes to bone. Metastases result in skeletal morbidity including pathologic fractures, the need for radiation or surgery to bone, spinal cord compression and hypercalcemia. The pathophysiology of bone destruction is related to activation of osteoclasts by tumor-derived and bone marrow microenvironmental factors. One prominent osteoclast-activating factor associated with breast cancer is parathyroid hormone-related peptide (PTHrP). Bisphosphonates have been shown to impair osteoclast activity by decreasing recruitment from the monocyte macrophage cell line, inhibiting osteoclast function at the bone site and causing osteoclasts to undergo apoptosis. Clinical studies with bisphosphonates show an improvement in the control of hypercalcemia and a reduction in skeletal related morbidity with administration of pamidronate and zoledronic acid. Bisphosphonates have become the standard of care for osteolytic metastases associated with breast cancer. Recent data with zoledronic acid found that skeletal related morbidity may be reduced regardless of the radiographic picture of skeletal metastases. Thus, zoledronic acid may be valuable in osteolytic and osteoblastic disease as well as in disease with an osteolytic or osteoblastic radiographic appearance. In breast cancer with osteolytic disease, zoledronic acid may be more effective than pamidronate in reducing skeletal morbidity and prolonging the time to first skeletal event.