"Their findings do provide reassurance for the safety of taking estrogen if a woman has had her ovaries out," said Dr. Rowan Chlebowski, a medical oncologist at the Los Angeles Biomedical Research Institute, who was not involved in the research. For women over 45, however, the hormone therapy is linked with a 20- to 26-percent jump in breast cancer risk.

"When you're in your mid-40s, you want to be more careful about the use of estrogen therapy," said Dr. Kala Visvanathan, one of the researchers on the study and a professor at Johns Hopkins Bloomberg School of Public Health in Baltimore.

Ovary removal, also called oophorectomy, is thought to decrease the risk of breast and ovarian cancer for some women. In certain cases, women at a high risk of cancer will get the surgery for prevention, while others will have it for reasons unrelated to cancer.

In younger women who have not experienced menopause, having the ovaries removed sends them into an abrupt menopause and can result in severe symptoms, such as hot flashes. Hormone replacement therapy (HRT) remains the most effective treatment for menopause symptoms.

But millions of women stopped using it after a large U.S. government study in 2002 found women taking estrogen and progestin, another hormone, had increased risks of heart attack, stroke and breast cancer.

Another part of the study that ended in 2004 found that women who had their uterus removed and who were taking estrogen alone also had an increased risk of stroke. There's been considerable discussion since then to calculate the risks and benefits of using hormone therapy to treat menopausal symptoms.

Visvanathan and her colleagues wanted to see whether estrogen therapy to relieve these symptoms would negate the benefits of having the ovaries removed. The idea is that removing the ovaries, and the estrogen produced by them, is responsible for the reduction in breast cancer risk.

"So the question is, if you elect to use estrogen therapy, will you have an increased breast cancer risk?" said Hazel Nichols, a researcher at the National Institute of Environmental Health Sciences in the Research Triangle Park, North Carolina, who also worked on the study.

REASSURING TO YOUNG WOMEN

The researchers collected survey information from more than 22,000 women. Nearly half had been diagnosed with breast cancer, while the rest of the women hadn't.

Overall, current estrogen users who had had both ovaries and their uterus removed had a 14-percent increase in breast cancer risk compared with women who experienced natural menopause and never used hormones.

Women who had the surgery done before age 40, however, had a smaller chance of getting breast cancer, whether or not they took estrogen, the researchers report in the medical journal Obstetrics and Gynecology.

The risk was 24 percent lower among those on the hormone, for example, than among women who had never had the surgery and hadn't used estrogen.

Chlebowski pointed out that the results apply only to women who had their ovaries and uterus removed; women who keep their uterus would take estrogen and progestin, which might give different results.

About one in eight American women develop breast cancer at some point in her life, although the majority survive, according to the American Cancer Society. Each year, according to the National Cancer Institute, 124 out of every 100,000 women develop the disease.

A 24 percent reduction in that number would mean 94 out of every 100,000 women would get the cancer. Women who had the surgery before 40 but who never used hormone therapy had an even greater drop in the risk of breast cancer - 30 percent.

"Part of the benefit of (the surgery) is probably being lost when a woman is using estrogen," said Dr. Graham Colditz, a professor at Washington University in St. Louis, who did not participate in the new research.

The gains from the surgery are only slightly diminished by hormone therapy, but Colditz said there is still a need for caution when using estrogen to treat menopause symptoms. The researchers found that the risk of breast cancer increased the older the women were at the time of surgery.

Nichols and her colleagues found that for women who had their ovaries and uterus removed after 50, taking estrogen was tied to a 26 percent increase in breast cancer risk. Nichols said there's a need for more research to help doctors best determine the risks and benefits of hormone therapy for each woman.

"I think what we've learned is that hormones shouldn't be prescribed to prevent chronic disease among healthy women, but there may be a role for them in treating severe symptoms (of menopause), and what we need to do now is to best understand what the safest way to do that is," she told Reuters Health.

SOURCE: bit.ly/Nl9HTE Obstetrics & Gynecology, July 2012.

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