Among healthy postmenopausal women at increased risk of breast cancer, the aromatase inhibitor Aromasin® (exemestane) reduces the risk of breast cancer but also increases bone loss. These results were published in Lancet Oncology.
Drugs that block the effects of estrogen have been shown to reduce the risk of breast cancer in women at high risk of the disease. Two drugs that have been approved for breast cancer risk reduction in certain groups of women are tamoxifen and Evista® (raloxifene). Tamoxifen is approved for breast cancer risk reduction in women who are at high risk of the disease (including high-risk premenopausal women). Evista—originally approved for the prevention and treatment of osteoporosis—is approved for breast cancer risk reduction in postmenopausal women with osteoporosis or postmenopausal women at high risk of breast cancer.
Aromatase inhibitors are drugs that block the production of estrogen in postmenopausal women. These drugs are commonly used in the treatment of hormone receptor-positive breast cancer, but may also have a role in breast cancer prevention. The preventive effect of the aromatase inhibitor Aromasin was evaluated in a Phase III clinical trial known as MAP.3. The study enrolled 4,560 postmenopausal women at increased risk of breast cancer. Women were treated with either Aromasin or a placebo, and the results indicated that Aromasin substantially reduced the likelihood of breast cancer.
Although aromatase inhibitors such as Aromasin provide breast cancer benefits, these drugs have also been reported to adversely affect bone. To explore the effects of Aromasin on bone among healthy women who use the drug for breast cancer prevention, researchers evaluated a subset of the women who participated in the MAP.3 trial. Information was available about 242 potmenopausal women who had been followed for two years.
Bone density was assessed using an advanced technique known as high-resolution peripheral quantitative CT. This technique is thought to provide more accurate and more informative measures of bone density than the commonly used dual-energy x-ray absorptiometry (DXA) scan.
During two years of treatment, bone density at the distal radius (wrist) decreased by 1.8 percent among women in the placebo group and by 6.1 percent among women in the Aromasin group. Other measures of bone density were also worse among women treated with Aromasin. The effect of these bone density changes on fracture risk will require longer follow-up.
These results demonstrate that use of Aromasin by healthy postmenopausal women increases bone loss. The benefit of Aromasin for breast cancer prevention will need to be weighed against its harmful effects on bone.
 Goss PE, Ingle JN, Ales-Martinez JE et al. Exemestane for breast-cancer prevention in postmenopausal women. New EnglandJournal of Medicine. 2011;364:2381-91.
 Cheung AM, Tile L, Cardew S et al. Bone density and structure in healthy postmenopausal women treated with exemestane for the primary prevention of breast cancer: a nested substudy of the MAP.3 randomised controlled trial. Lancet Oncology. Early online publication February 7, 2012.
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