According to results presented at the 2006 annual meeting of the American Society of Clinical Oncology (ASCO), women who are treated with the aromatase inhibitor Arimidex® (anastrozole) experience bone loss. However, this bone loss is not likely to cause osteoporosis in women with normal bone density before beginning therapy.
Arimidex, as well as other aromatase agents, is commonly used in the treatment of postmenopausal, hormone-positive breast cancer.
Although survival is significantly improved with the use of aromatase agents, side effects from these agents continue to be evaluated. There has been concern that long-term use of aromatase agents will potentially reduce bone density and increase bone fractures.
Researchers continue to try to identify specific variables-such as duration of treatment-that may place some patients at a high risk for developing osteoporosis or suffering from bone fractures. In addition, researchers are investigating potential ways to minimize or prevent this risk.
Researchers recently evaluated results from the ATAC trial, in which postmenopausal women with hormone-positive, early breast cancer were treated with Arimidex or Nolvadex® (tamoxifen) for five years. Both groups were directly compared.
- Women taking Arimidex had a 6%-7% loss of bone mineral density.
- The fracture rate was 11% for women taking Arimidex, compared with 7.7% for those taking tamoxifen.
- The risk of bone fractures declined once women stopped taking Arimidex.
- Researchers stated that a 6%-7% loss of bone mineral density should not be enough to cause osteoporosis among women with normal bone density levels when they begin treatment (baseline).
- Researchers are advocating the evaluation of bisphosphonates and exercise, particularly weight-bearing exercise, in women taking aromatase as potential ways to minimize loss of bone mineral density in these patients.
The researchers concluded that treatment with five years of Arimidex results in loss of bone mineral density and increases the risk of bone fractures among postmenopausal women with early breast cancer. However, they suggest that the reduction in levels should not cause osteoporosis among women with normal baseline bone density, and the risk of fractures declines once patients discontinue treatment with the drug.
Reference: Coleman R, et al. Effect of anastrazole on bone mineral density: 5-year results form Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial. Proceedings from the 42nd annual meeting of the American Society of Clinical Oncology. June 2006. Atlanta, GA. Abstract 511.
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