What is the role of aromatase inhibitors for women with breast cancer?

Aromatase inhibitors decrease estrogen levels in postmenopausal women and can reduce a woman's risk of recurrence following surgery for early, hormone-dependent breast cancer. Current studies have shown that the use of an aromatase inhibitor (either as initial therapy or after tamoxifen) results in a modest decrease in the chance of recurrence.

Large clinical trials have shown that in postmenopausal women with hormone receptor-positive, Stage I, II, and III breast cancer, the aromatase inhibitors can add to the benefits that are seen with tamoxifen, another anti-estrogen therapy. As a result, experts have recommended that women consider taking one of the three commercially available aromatase inhibitors: Arimidex, Aromasin, and Femara. There are two strategies that are reasonable at this time—either an aromatase inhibitor for five years, or two years of tamoxifen followed by an aromatase inhibitor for 3-5 years.

For selected women who are at very low risk of recurrence or for those who have intolerable side effects with the aromatase inhibitors, treatment with tamoxifen alone remains a possibility. The side effects and adverse consequences of tamoxifen and the aromatase inhibitors vary. Tamoxifen can cause hot flashes and a vaginal discharge and is also associated with a slightly increased risk of blood clots in the veins as well as a slightly increased risk of endometrial cancer. The aromatase inhibitors can also cause hot flashes but are not associated with blood clots or endometrial cancer. However, the aromatase inhibitors increase the risk of osteoporosis and fractures and are also associated with joint pains.

Ongoing studies are attempting to determine if one aromastase inhibitor is better than another. Studies are also looking at whether more than five years of an aromatase inhibitor is safe and whether more prolonged treatment can reduce breast cancer recurrence rates. With longer follow-up, it is possible that more substantial benefits will be seen. Studies are also trying to determine if tamoxifen or the aromatase inhibitors are of particular benefit in specific subgroups of patients. Ultimately, it is hoped that we will be able to individualize therapy based on the characteristics of woman’s tumor and other patient factors.

Answer provided by:
Eric P. Winer, MD 
Chief, Division of Women’s Cancers, Director, Breast Oncology at Dana-Farber/Brigham and Women’s Cancer Center
Professor of Medicine at Harvard Medical School
Boston, Massachusetts