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Breast Cancer Health Center

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Menopause Treatment a Cancer Risk?

Study Shows Estrogen Plus Testosterone May Up Risk of Breast Cancer
WebMD Health News
Reviewed by Louise Chang, MD

July 24, 2006 -- Women who take the hormones estrogen and testosterone to combat hot flashes, decreased libido, and other symptoms of menopausemay be at an increased risk of developing breast cancer, say researchers.

Older studies have shown that estrogen plus progesterone increases breast cancerrisk, but until now there has been little research on what effect testosterone has on such risk. While considered the male sex hormone, women, too, have testosterone and as they age, their natural levels decline.

Some evidence suggests that many of the symptoms of menopause -- including decreased sex drive, worse moods, and poorer quality of life -- may be related to a decline in testosterone. And the use of testosterone as part of hormone replacement therapy appears to be on the rise. The number of women in the study who used estrogen-plus-testosterone therapy increased dramatically from 33 in 1988 to 550 in 1998.

Long-Term Effects of Hormone Therapy

In the new study, in the July 24 issue of the Archives of Internal Medicine, researchers led by Rulla M. Tamimi, ScD, of Brigham and Women's Hospital and Harvard Medical School in Boston, and colleagues studied the long-term effects of estrogen-plus-testosterone therapy in 121,700 women who were part of the Nurses' Health Study. The women completed an initial questionnaire and follow-up surveys every two years that included questions about menopausal status, medical conditions, and the use of hormone therapy.

There were 4,610 cases of breast cancer among postmenopausal women during 24 years of follow-up. Women who were currently taking estrogen plus testosterone had a 77% higher risk of developing breast cancer than those who had never used hormone therapy. By contrast, women currently using estrogen showed a 15% increased risk of breast cancer and those who were taking estrogen plus progesterone had a 58% increased risk of breast cancer.

What's more, women who had gone through menopause naturally and took estrogen plus testosterone had 2.5 times the risk of breast cancer than those who had never used hormone therapy. Estrogen-only therapy showed a 23% increased risk and estrogen-plus-progesterone therapy was linked to a 66% increased risk in those women with natural menopause.

Exactly how testosterone may increase the risk of breast cancer is not fully understood, but researchers speculate that enzymes in the breast tissue may convert testosterone to estradiol, an estrogen-like hormone that may contribute to the development of breast cancer.

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