The aromatase inhibitor Aromasin® (exemestane) reduces the risk of breast cancer in postmenopausal women at increased risk of the disease. The results of this Phase III trial were presented at the 2011 annual meeting of the American Society of Clinical 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. Aromatase inhibitors include Arimidex® (anastrozole), Femara® (letrozole), and Aromasin® (exemestane).
To evaluate Aromasin for breast cancer prevention in high-risk women, researchers conducted a Phase III trial among 4,560 postmenopausal women. The women had at least one of these breast cancer risk factors: 1) age greater than 60; 2) five-year risk of breast cancer of more than 1.66% based on the Gail score; 3) prior atypical ductal or lobular hyperplasia, lobular carcinoma in situ, or ductal carcinoma in situ with mastectomy.
Study participants received either Aromasin or a placebo, and have now been followed for an average of three years.
- Risk of invasive breast cancer was 65% lower among women in the Aromasin group than among women in the placebo group. There were 11 invasive breast cancers in the Aromasin group and 32 invasive breast cancers in the placebo group.
- Symptoms such as hot flashes, fatigue, sweating, insomnia, and joint pain were common among all study participants, but slightly more so among women treated with Aromasin.
These results suggest that Aromasin may be safe and effective when used to reduce the risk of breast cancer in high-risk women. Aromasin has not yet been approved for this purpose.
Reference: Goss PE, Ingle JN, Ales-Martinez J et al. NCIC CTG MAP.3: A Phase III placebo-controlled Breast Cancer Prevention Trial of exemestane in postmenopausal women at risk for breast cancer. Paper presented at: 2011 Annual Meeting of the American Society of Clinical Oncology; June 3-7, 2011; Chicago, IL. Abstract LBA504.
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