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Estrogen-Only HRT Safe for 15 Years

After Hysterectomy, Breast Cancer Risk Rises Only After 15 Years of HRT
By
WebMD Health News
Reviewed by Louise Chang, MD

May 8, 2006 -- Estrogen-only hormone therapy taken after hysterectomy ups a woman's risk of breast cancer -- but only after 15 years of treatment.

The reassuring news comes from nearly 29,000 women enrolled in the Nurses' Health Study. It reinforces a recent report from the Women's Health Initiative finding no increased risk of breast cancer after more than seven years of estrogen-only hormone therapy.

The finding applies just to estrogen-only HRT prescribed for women who have had a hysterectomy (removal of the uterus). For women with a uterus, estrogen alone greatly increases the risk of uterine cancer. To avoid this risk, HRT for women with a uterus balances estrogen with progesterone. But adding progesterone to estrogen increases the risk of breast cancer.

15 Years of Treatment

Women who keep taking estrogen-only HRT for 15 years or longer do up their risk of breast cancer.

Study leader Wendy Y. Chen, MD, MPH, is an oncologist at Brigham and Women's Hospital and Dana Farber Cancer Institute, Boston. "In long-term users of estrogen, after 15 years there was a statistically significant increased risk in hormone-receptor-positive breast cancers," Chen tells WebMD. "After 20 years, there was a significantly increased risk for all types of breast cancer."

Chen and colleagues report the findings in the May 8 issue of Archives of Internal Medicine.

How Much Breast Cancer Risk?

Some breast cancers grow faster in the presence of the sex hormones estrogen and progesterone. Only these hormone-sensitive breast cancers were seen 48% more often in women taking estrogen HRT for 15-20 years. Women who took estrogen-only HRT for 20 years or more had a 73% higher risk of hormone-sensitive breast cancer than women who never used HRT.

That's still not a huge increase in risk, says Hugh Taylor, MD, director of the menopause program at Yale University. Taylor has received speakers' fees from -- but has no financial interest in -- Wyeth Pharmaceuticals, the maker of Premarin and Prempro HRT products. Wyeth is a WebMD sponsor.

"This is a very small risk," Taylor tells WebMD. "An increase of about 50% after 15 years is still a relatively small number of breast cancers."

The risk tended to concentrate in thinner women -- those with a body mass index under 25. That finding was what researchers call a "trend." It could have been chance, but there's good reason to think it is real.

"Heavier women are well known to have higher levels of estrogen, because fat tissue converts other things in your body into estrogens," Chen says. "It's the same reason why birth control pills, which contain much more estrogen than HRT, aren't linked to breast cancer. That is because before menopause, a woman has a lot of estrogen, and adding a lot of estrogen doesn't affect her hormone balance as much as adding a little estrogen affects a postmenopausal woman who doesn't have as much in her body."

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