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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 1 (Arimidex®), exemestane 2 (Aromasin®), and letrozole 3 (Femara®).
- Denosumab May Help Prevent Bone Loss Related to Use of Aromatase Inhibitors 4
(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 5
(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. - Study Confirms Risk of Bone Loss for Patients Taking Exemestane 6
(Posted: 02/14/2007) - Women who switched to the drug exemestane after taking tamoxifen to prevent a breast cancer relapse lost more bone density and had a higher risk of bone fractures than women who continued taking tamoxifen, according to a report published online Jan. 26, 2007, by Lancet Oncology. - Zoledronic Acid Prevents Bone Loss During Estrogen-Suppression Treatment of Breast Cancer 7
(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. - Advanced Breast Cancer Patients Benefit More from Aromatase Inhibitors than Tamoxifen 8
(Posted: 10/10/2006) - Researchers analyzed published clinical trials and found that third-generation aromatase inhibitors provide a definite, if small, overall survival advantage compared to tamoxifen for patients with advanced breast cancer, according to the Sept. 20, 2006, Journal of the National Cancer Institute. - Anastrozole May Be Better than Tamoxifen at Shrinking Large Breast Tumors Before Surgery 9
(Posted: 08/30/2005) - In this small trial of postmenopausal women with estrogen-receptor positive, early stage breast cancer, anastrozole (Arimidex®) appeared to do better than tamoxifen (Nolvadex®) at shrinking large tumors prior to surgery. - Anastrozole After Tamoxifen Better for Early Breast Cancer than Tamoxifen Alone 10
(Posted: 08/30/2005, Reviewed: 02/14/2007) - In published reports from two similar clinical trials, researchers show that switching certain breast cancer patients at two years from the standard post-surgery treatment tamoxifen to another drug called anastrozole provides more protection against recurrence. - Anastrozole Reduces Recurrence in Early Breast Cancer: 10-Year Results of the ATAC Trial 11
(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. - Study Confirms Letrozole Prevents More Breast Cancer Recurrences than Tamoxifen 12
(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. - New Treatment Significantly Improves Long-Term Outlook for Breast Cancer Survivors:
International clinical trial concludes women should consider taking letrozole after five years of tamoxifen treatment to continue to reduce risk of recurrence 13
(Posted: 10/09/2003, Updated: 06/10/2004) - A Canadian-led international clinical trial has found that post-menopausal survivors of early-stage breast cancer who took the drug letrozole after completing an initial five years of tamoxifen therapy had a significantly reduced risk of cancer recurrence compared to women taking a placebo. Questions and Answers 14 - Exemestane Following Tamoxifen Reduces Breast Cancer Recurrences and Prolongs Survival 15
(Posted: 03/10/2004, Updated: 06/04/2006) - Longer follow-up data from a large international phase III trial of postmenopausal women with breast cancer who switched to the drug exemestane (Aromasin®) after several years on tamoxifen confirm a delay in disease progression and also show a survival advantage, compared to women who stayed on tamoxifen, according to findings presented at the 2006 meeting of the American Society of Clinical Oncology. - Fulvestrant: New Treatment Option for Advanced Breast Cancer 16
(Posted: 08/26/2002, Reviewed: 10/04/2006) - A new drug called fulvestrant (Faslodex) was as effective as another drug, anastrozole (Arimidex), in postmenopausal women with advanced, previously treated breast cancer, according to two studies published in the August 15, 2002, issue of the Journal of Clinical Oncology.