The link between hormone therapy (HT) for menopausal women and breast cancer risk has been researched extensively, and now a new study has found any type of hormone therapy -including estrogen alone - may raise a woman’s breast cancer risk if she takes it for more than 10 years.

It is already known that taking pills that combine estrogen and progestin - the most common type of hormone therapy - can increase breast cancer risk. But women who no longer have a uterus can take estrogen alone, which was thought to be safe and possibly even slightly beneficial in terms of cancer risk.

The new study suggests otherwise, if the pills are used for many years. It tracked the health of about 60,000 nurses and found that use of any kind of hormones for 10 years or more slightly raised the chances of developing breast cancer.

“What we found is that people should also be careful about longer-term use of estrogen-alone HT,” study author Dr. Wendy Chen, an assistant professor in medicine at the Dana-Farber Cancer Institute in Boston, Mass., said in a written statement.

Chen found breast cancer risk was 88 percent higher in women who had taken estrogen plus progesterone for 10-15 years, compared with women who didn’t use hormone therapy. Breast cancer risk doubled for women who were on that type of therapy 15 to 20 years. The cancer risk never tapered off and kept increasing, the researchers found.

“There’s a continued increase in risk with longer durations of use and there does not appear to be a plateau,” Chen said

The study was discussed Sunday at a cancer conference in Chicago.

The hormone picture has been confusing, and the absolute risk of breast cancer for any woman taking hormone pills remains small. Doctors say women should use the lowest dose needed for the shortest time possible.

“It’s hard to be surprised that if you keep taking it, sooner or later it’s going to raise risk,” said Dr. Robert Clarke of Georgetown University’s Lombardi Comprehensive Cancer Center.

The link between breast cancer risk and estrogen therapy dates back to the 1990s, when a large U.S. funded study, known as the Women’s Health Initiative, began tracking the effects of estrogen-progestin combination pills and estrogen-only therapies. The estrogen-progestin part of the study was stopped in 2002 when the combo pill was linked to higher risks for heart attacks and breast cancer. In 2004, the estrogen study was halted after researchers detected stroke and blood clot risks in that group.

Last month, a study in Lancet Oncology found menopausal women taking estrogen actually had a reduced risk for breast cancer, HealthPop reported. Some experts commented that the study was “inconsistent” with the totality of evidence.

What should women do?

Chen told HealthDay women should think about why they’re taking these hormones to begin with, and a doctor might be able to prescribe something else.

“If it is for hot flashes, they don’t last forever,” she told HealthDay. 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.

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By CBS News Staff