The drug therapy of postmenopausal osteoporosis includes hormone replacement therapy, selective oestrogen receptor modifiers (SERMS) and bisphosphonates. Unlike hormone replacement therapy and SERMS bisphosphonates do not carry the risk of breast cancer. In fact, in vitro studies have shown that bisphosphonates may have an anti-cancer effect and this effect may not be limited to bone metastasis. There are two classes of bisphosphonates nitrogen containing (alendronate, risedronate, zoledronate and ibandronate) and those without nitrogen (clodronate, etidronate). Nitrogen containing bisphosphonates have anti-cancer properties. Are women receiving bisphosphonates for osteoporosis protected from cancer?
Two recently published studies suggest that bisphosphonates taken for osteoporosis reduce the risk of cancer. The Women’s Health Initiative Observational Study, that included 154,768 women receiving bisphosphonates for osteoporosis suggest that bisphosphonates reduce the risk of breast cancer by 32%. The Breast Cancer in Northern Israel Study showed a 28% risk reduction in breast cancer in receiving bisphosphonates for osteoporosis. An earlier study has shown a 33% reduction in breast cancer with the use of bisphosphonates.
Breast cancer is one of the most common cancers in women. Breast cancer accounts for about one million cancers per year. Bisphosphonates could prevent 300,000 of these. Should bisphosphonates be used for chemoprophylaxis of breast cancer?
Bisphosphonates are associated with rare serious adverse effects including gastric and oesophageal ulcers, jaw necrosis and possible atrial fibrillation and increased risk of oesophageal carcinoma. Use of bisphosphonates for chemoprophylaxis of breast cancer would expose normal individuals to this risk. Unless the benefits of bisphosphonates in breast cancer prevention are documented in a controlled trial, bisphosphonates can not be recommended for use in prophylaxis of breast cancer. However the reduction in the risk of breast cancer may be a reason of choosing bisphosphonates over other drug therapy for osteoporosis.