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Many breast tumors are "estrogen sensitive," meaning the hormone estrogen helps them to grow. Aromatase inhibitors (AIs) can help block the growth of these tumors by lowering the amount of estrogen in the body.
Estrogen is produced by the ovaries and other tissues of the body, using a substance called aromatase. AIs do not block estrogen production by the ovaries, but they can block other tissues from making this hormone. That's why AIs are used mostly in women who have reached menopause, when the ovaries are no longer producing estrogen.
Another drug, tamoxifen (Nolvadex®), also helps to prevent the growth of estrogen-sensitive breast tumors, but it works differently from AIs. Whereas AIs reduce the amount of estrogen in the body, tamoxifen blocks a tumor's ability to use estrogen.
Currently, three AIs are approved by the U.S. Food and Drug Administration: anastrazole (Arimidex®), exemestane (Aromasin®), and letrozole (Femara®).
- Study Confirms Letrozole Prevents More Breast Cancer Recurrences than Tamoxifen
(Posted: 12/02/2011) - After a median of 8 years of follow-up from a large randomized trial, women with estrogen-receptor positive breast cancer who received 5 years of treatment with letrozole were less likely to have their cancer recur or to die during follow-up than women who had 5 years of treatment with tamoxifen. - Anastrozole Reduces Recurrence in Early Breast Cancer: 10-Year Results of the ATAC Trial
(Updated: 12/30/2010) - Anastrozole (Arimidex®) is better than tamoxifen (Nolvadex®) at preventing a recurrence of breast cancer in postmenopausal women with early-stage hormone receptor-positive tumors, according to a report published in Lancet Oncology on November 17, 2010. - Zoledronic Acid Prevents Bone Loss During Estrogen-Suppression Treatment of Breast Cancer
(Posted: 01/09/2007, Updated: 09/16/2008) - Zoledronic acid can prevent treatment-induced bone loss in premenopausal women undergoing total estrogen suppression after surgery for hormone-responsive breast cancer, according to an article published online Jan. 3, 2007, in the Journal of Clinical Oncology. - Denosumab May Help Prevent Bone Loss Related to Use of Aromatase Inhibitors
(Posted: 09/11/2008) - Treatment with the experimental drug denosumab increased bone density in postmenopausal women taking aromatase inhibitors to prevent a recurrence of breast cancer, according to a report published online August 25, 2008, by the Journal of Clinical Oncology. - Aromatase Inhibitors Come of Age
(Posted: 03/07/2007) - Aromatase inhibitors (AIs), which interfere with the body's ability to produce the hormone estrogen, are rapidly changing the standard of treatment for breast cancer. Researchers have now taken up the challenge of learning how and when to best use these drugs.