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In addition to increasing the likelihood of breast cancer, postmenopausal hormone therapy with estrogen plus progestin may also be linked with more advanced breast cancers. These findings were recently published in the Journal of the American Medical Association.

As women reach menopause and beyond, more than 80% will experience symptoms such as hot flashes, night sweats, sleep disturbance, and vaginal dryness. Estrogen, with or without progestin, is an effective treatment for many of these symptoms. Over the last several years, however, studies have raised important concerns about the health effects of menopausal hormone therapy.

In 2002, a report from the Women’s Health Initiative (WHI) indicated that combined hormone therapy increased the risk of breast cancer, heart disease, stroke, and blood clots.  Use of combined hormone therapy decreased the risk of fractures and colorectal cancer, but these benefits were thought to be outweighed by the risks for most women.

After this report, use of combined hormone therapy declined markedly. Studies from several countries—including the United States—suggest that this decline in hormone use was followed by a decline in breast cancer incidence rates.

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Using participants and data from a WHI trial evaluating combined hormone therapy and breast cancer incidence, researchers recently reported longer-term results on breast cancer, including data on mortality. The original trial included 16,608 postmenopausal women and compared outcomes of combined hormone therapy versus placebo; findings indicated an increase in breast cancer incidence among those receiving combined hormone therapy. When this trial concluded, participants were asked if they’d consent to continued follow-up. Follow-up data were obtained for 12,788 women. Study participants have now been followed for an average of 11 years.

  • Combined hormone therapy was associated with greater breast cancer incidence than placebo: risk of breast cancer was 0.42% per year among women in the hormone therapy group compared with 0.34% per year among women in the placebo group.
  • Breast cancers among women receiving combined hormone therapy were more likely to be node-positive than among those receiving placebo. Twenty-four percent of breast cancers in the hormone therapy group were node-positive, compared with 16% among women in the placebo group.
  • There were more breast cancer deaths among those receiving combined hormone therapy than among those receiving placebo, but this finding was of borderline statistical significance, suggesting that it could have occurred by chance alone. Similar results were found for all-cause mortality.

The researchers concluded that among postmenopausal women, combined hormone therapy with estrogen plus progestin increases breast cancer incidence and the risk of node-positive breast cancer, and may also increase breast cancer mortality.

Reference: Chlebowski RT, Anderson GL, Gass M, et al. Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women. JAMA. 2010;304(15):1684-1692. doi:10.1001/jama.2010.1500.

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