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Postmenopausal women who take hormone therapy consisting of estrogen alone may have a reduced risk of developing or dying from breast cancer. These findings—from longer-term follow-up of the Women’s Health Initiative trial of estrogen alone—were published in Lancet Oncology. It should be noted that this report addressed only estrogen alone; it did not include combined estrogen plus progestin, which has previously been linked with an increased risk of breast cancer.

Menopause—when menstrual cycles end and ovarian hormone production drops dramatically—produces symptoms such as hot flashes and night sweats in up to 80% of women. When these symptoms are severe, they can have a profound effect on a woman’s quality of life and ability to function.

For many years, hormone therapy with estrogen (with or without progestin) has provided an effective way for women to manage menopausal symptoms. Studies over the last several years, however, have raised some concerns about the health effects of 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]

Initial reports from the WHI study of estrogen alone found that 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 only used in women who have had a hysterectomy.

In 2011, updated results from the study of estrogen alone suggested that estrogen may actually reduce the risk of breast cancer.[4] These results were further explored in the current analysis. Information was available about 7,645 postmenopausal women who had been followed for a median of close to 12 years.[5]

  • Compared with women in the placebo group, women in the estrogen group were 23 percent less likely to develop invasive breast cancer. Estrogen was also linked with a reduced risk of dying from breast cancer.
  • The reduced risk of breast cancer among estrogen users was only seen in women who were not at increased risk of breast cancer to start with. Among higher-risk women (those who had a history of benign breast disease or a family history of breast cancer), estrogen did not reduce the risk of breast cancer.

These results should be reassuring to women who have had a hysterectomy and choose to use estrogen alone to manage menopausal symptoms: estrogen alone does not appear to increase the risk of breast cancer and may actually decrease risk. This potential benefit of estrogen does not appear to apply to women at increased risk of breast cancer. Furthermore, any potential benefits of estrogen must be weighed against the risks.

Women who are considering using hormone therapy to manage menopausal symptoms are advised to discuss the risks and benefits with their physician.

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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] LaCroix AZ, Chlebowski RT, Manson JE et al. Health outcomes after stopping conjugated equine estrogens among postmenopausal women with prior hysterectomy: a randomized controlled trial. JAMA. 2011;305:1305-1314.

[5] Anderson GL, Chlebowski RT, Aragaki AK et al. Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women’s Health Initiative randomised placebo-controlled trial. Lancet Oncology. Early online publication March 7, 2012.

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