SUNDAY, April 1 (HealthDay News) -- Several weeks after a study suggested that women who take estrogen-only hormone replacement to treat menopause symptoms may be at lower risk for developing breast cancer, another, much-larger study finds that when used for longer than 10 years, estrogen-only regimens actually raise a woman's long-term risk for breast cancer.

The new study was funded by the National Cancer Institute, part of the U.S. National Institutes of Health, whereas the previous one was partially funded by drug manufacturer Wyeth.

Researchers evaluated follow-up data from the Nurse's Health Study collected from 1980 through 2008. The women in the study were 30 to 55 years old in 1976. Overall, the risk for breast cancer was 88 percent higher among women who had taken estrogen plus progesterone for 10 to 14.9 years, compared to women who did not. This risk more than doubled for women who used estrogen-plus-progesterone therapy for 15 to 19.9 years.

Women who used estrogen-only therapy after menopause had 22 percent increased risk for breast cancer if they used it for 10 to 14.9 years, and 43 percent greater risk if they used it longer than 15 years.

There was no increased risk seen among women who took estrogen for fewer than 10 years. Women did not have an increased risk of dying from breast cancer, the study showed.

Hormone replacement therapy (HRT) fell from grace after the U.S. Women's Health Initiative study was stopped early in 2002 because HRT was shown to increase the risk of strokes and breast and ovarian cancer. Some subtleties have emerged since that time. For example, short-term use of HRT is now deemed fairly safe for some women who have severe menopausal symptoms. Estrogen-only therapy is reserved for women who have had a hysterectomy; women with an intact uterus who use HRT must take the hormone progestin (synthetic progesterone) with estrogen to prevent uterine cancer.

"For combination therapy there is so much data about the dangers that we really tell people that if they must take it to treat symptoms, they should only do so for a year or two at most," said study author Dr. Wendy Chen, an associate physician at Brigham and Women's Hospital and an assistant professor in medicine at the Breast Cancer Treatment Center at the Dana-Farber Cancer Institute in Boston. "For estrogen alone, there is more safety data for someone who wants to take it for five or six years."

Chen is scheduled to present her findings at this week's annual meeting of the American Association for Cancer Research in Chicago.

Her advice is for women to think about why they are taking supplemental hormones. "If it is for hot flashes, they don't last forever," she said. If vaginal dryness is the issue, there are vaginal hormone preparations. "You are not going to have the systemic effects that you will from talking a pill," she said.

Dr. Larry Norton, deputy physician-in-chief for breast cancer programs at Memorial Sloan-Kettering Cancer Center and medical director of the Evelyn H. Lauder Breast Center, in New York City, does not recommend that women take estrogen after menopause.

"The jury is still out on how safe estrogen alone is, but I am not recommending it, and the major reason why is because every drug I know that reduces the risk of breast cancer reduces estrogen," he said. "Saying an estrogen is going to be safe raises an important question mark in my mind," Norton said. "Alternative treatments may help treat the symptoms and risks associated with menopause, so why take the chance?"

Because the new study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

Learn more about the benefits and risks of HRT through the North American Menopause Society.