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Among women at low risk of breast cancer, postmenopausal hormone therapy with estrogen alone may reduce the risk of breast cancer. These results—which warrant additional research and should not be considered conclusive—came from further review of the Women’s Health Initiative clinical trial of estrogen alone and were presented at the 2010 San Antonio Breast Cancer Symposium (SABCS).

Hormone therapy with estrogen (with or without progestin) effectively manages many menopausal symptoms, but studies over the last several years have raised concerns about the health effects of postmenopausal hormone therapy. In the Women’s Health Initiative (WHI) clinical trial of estrogen plus progestin, hormone use decreased the risks of fracture and colorectal cancer, but increased the risks of heart disease, breast cancer, stroke, and blood clots.[1] More recent reports suggest that combined hormone therapy may also increase lung cancer mortality.[2]

Estrogen alone did not appear to increase the risk of breast or lung cancer but did increase risk of stroke.[3]Because estrogen alone increases the risk of endometrial (uterine) cancer, it is generally reserved for women who have had a hysterectomy.

In the results presented at SABCS, researchers evaluated subgroups of women enrolled in the WHI trial of estrogen alone.[4]

  • In the subgroups of women at low risk of breast cancer (women without a strong family history of breast cancer and women without a personal history of breast disease), use of estrogen alone was linked with a reduced risk of breast cancer.
  • Among younger women (those under the age of 60), there was a suggestion that the benefits of estrogen alone may outweigh the risks for many women.

These results were discussed at a press conference moderated by Judy Garber, MD, MPH. Dr. Garber described the results as “provocative and preliminary.” Further research is required before firm conclusions can be drawn about the relationship between estrogen alone and risk of breast cancer.

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[1] Rossouw JE, Anderson GL, Prentice RL et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women’s Health Initiative randomized controlled trial. JAMA. 2002; 288:321-33

[2] Chlebowski RT, Schwartz AG, Wakelee H et al. Oestrogen plus progestin and lung cancer in postmenopausal women (Women’s Health Initiative trial): a post-hoc analysis of a randomised controlled trial. Lancet. 2009;374:1243-1251.

[3] Anderson GL, Limacher M, Assaf AR et al. Effects of conjugated equine estrogen in postmenopausal women with hysterectomy: the Women’s Health Initiative randomized controlled trial. JAMA. 2004; 291:1701-1712.

[4] Ragaz J, Bajdik C, Wilson KS et al. Dual estrogen effects on breast cancer: endogenous estrogen stimulates while exogenous estrogen protects. Presented at the 33rd annual San Antonio Breast Cancer Symposium, December 8-12, 2010.

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