According to the results of a Phase III clinical trial presented at the 2007 San Antonio Breast Cancer Symposium, the experimental drug denosumab significantly improves bone density among women with non-metastatic breast cancer treated with an aromatase inhibitor.
Each year breast cancer is diagnosed in over 178,000 women in the United States alone. Many of these breast cancers will be hormone receptor-positive, meaning that they are stimulated to grow by the circulating female hormones estrogen and/or progesterone.
Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen. These therapies include tamoxifen as well as agents known as aromatase inhibitors. Tamoxifen acts by blocking estrogen receptors, whereas aromatase inhibitors suppress the production of estrogen in postmenopausal women.
Although several studies have shown that aromatase inhibitors reduce the risk of breast cancer recurrence among postmenopausal breast cancer patients, they have been linked with bone loss. Use of drugs that reduce bone loss may therefore benefit women who are treated with an aromatase inhibitor.
Denosumab is an experimental drug that is given as a twice yearly subcutaneous injection. To evaluate the effects of denosumab on bone density among women treated with an aromatase inhibitor, researchers conducted a Pase III clinical trial. The trial enrolled 252 women with non-metastatic, hormone receptor-positive breast cancer. At the start of the study, all study participants had evidence of bone loss but none had osteoporosis.
All of the study participants were receiving adjuvant treatment with an aromatase inhibitor. Half the women received four doses of denosumab and half received a placebo. All patients were asked to take calcium and vitamin D supplements.
- Compared to patients in the placebo group, patients in the denosumab group had 5.5% higher lumbar spine bone density at 12 months of follow-up.
- Women treated with denosumab also had higher total hip bone density and higher total body bone density.
- The overall frequency of adverse events was similar in the denosumab group and the placebo group.
These results suggest that denosumab effectively improves bone density among breast cancer patients receiving adjuvant aromatase inhibitor therapy.
Reference: Ellis G, Bone HG, Chlebowski R et al. A phase 3 study of the effect of denosumab therapy on bone mineral density in women receiving aromatase inhibitors for non metatastatic breast cancer. Presented at the 30th Annual San Antonio Breast Cancer Symposium. San Antonio, TX, December 13-16, 2007. Abstract #47.