Study looks at denosumab in preventing bone loss caused by aromatase inhibitors

Denosumab is a new drug being studied to prevent fractures in breast cancer patients receiving hormonal therapy.

Results of a phase 3 clinical trial using denosumab were presented Friday evening at the San Antonio Breast Cancer Symposium by Georgiana Ellis, MD, from the Seattle Cancer Care Alliance.

Denosumab is a highly specific antibody that interrupts the development of osteoclasts -- specialized cells that break down bone. Because it is highly specific, the chance of systemic effects in other parts of the body is low, so patients do not need routine laboratory monitoring.

A group of drugs called aromatase inhibitors is used to prevent the recurrence of breast cancer in postmenopausal women. These drugs are very effective, but commonly associated with loss of bone density and an increased risk of fractures.

To test the effectiveness of denosumab in preventing bone loss caused by aromatase inhibitors, a clinical trial recruited 252 patients who had been treated for early stage breast cancer and for whom treatment with anastrozole, an aromatase inhibitor, was planned. Half of the patients were given denosumab, while the other half was not. All patients were instructed to take daily doses of calcium and vitamin D.

The study lasted for 2 years, with patients receiving an injection of denosumab every 6 months. All the women from both groups had their lumbar spine bone density measured at the end of the first and second years. By the end of the first year, the bone density of the women receiving denosumab had increased by nearly 5%, while the women who did not receive denosumab had bone density decreases of almost 1%. By the end of the second year, the difference was even greater: in the women receiving denosumab, bone density had increased by almost 6%, while the bone density of the women who did not receive denosumab decreased by nearly 2%. Similar effects on bone density were seen at the hip and the wrist. Side effects of denosumab were similar to those reported in the control group.

Denosumab appears to be a safe and effective treatment for preventing bone loss in women taking aromatase inhibitors, offering an alternative to existing therapies, such as oral or intravenous bisphosphonates.