Estrogen-Only Hormone Replacement Therapy May Cut Breast Cancer Risk

Women who take only estrogen, instead of estrogen and progesterone, as their hormone replacement therapy for the symptoms of menopause don't increase their risk of breast cancer but actually reduce it, according to new research.

The discovery was based on a re-analysis of the data of a Women's Health Initiative study and the finding that they did not apply to women younger than 60, study researcher Dr. Joseph Ragaz explained.

Doctors currently warn women not to take hormone replacement therapy including progesterone and estrogen for long terms because of the increased risks of developing ovarian, breast or endometrial cancer, as revealed in the WHI study.

But Ragaz, a medical oncologist and professor at the University of British Columbia, and his colleagues re-examined the data and found that women who took estrogen alone had a 20 percent lower risk of developing breast cancer than women who didn't take any form of hormone replacement therapy.

And among women who had no family history of the disease and who had not previously had breast cancer themselves , the risk was 30 to 40 percent lower, Ragaz said.

For women younger than 60, "hormone replacement therapy with estrogen alone is very safe and beneficial, and should be recommended for menopause management, Ragaz told MyHealthNewsDaily.

The research was presented today (Dec. 9) at the annual San Antonio Breast Cancer Symposium.

Taking a second look

Ragaz and his colleagues re-analyzed the data from two clinical trials in the WHI study. The first trial, which examined the effects of taking progesterone plus estrogen, was stopped earlier than planned, in 2002, because it became apparent that women on the therapy faced heightened cancer risks, according to the National Cancer Institute.

Eleven years after that trial started, researchers found that taking estrogen and progesterone combined increased breast cancer risk 1.25 times, and doubled a woman's risk of dying from breast cancer, according to a study published in October in the Journal of the American Medical Association.

The second WHI trial, which examined the effects of taking only estrogen, was also stopped early than planned, in 2004, after seven years of data showed elevated risks for blood clots and stroke risk in the patients.

However, Ragaz found that two-thirds of the women in that estrogen-only trial were over the age of 60. When he looked at the data from women who started the treatment before age 60, he saw no increased risks for stroke or clotting, and no adverse effects on the heart. At the same time, these women showed improved bone density and a decreased risk of colon cancer, Ragaz said.

Different estrogen

Not all estrogen is alike. Ragaz and his colleagues found differences between estrogen produced from women's ovaries and the estrogen used in hormone replacement therapy. Estrogen produced in the body can be cancer-causing for some women, but it seems the estrogen in hormone replacement therapy has a protective effect, he said.

This estrogen can "counteract, beneficially, the negative aspect of the estrogen " naturally produced in the body, Ragaz said.

More research is needed to determine how much estrogen is necessary to achieve that protective effect, and how long it must be taken, he said.

Pass it on: Not all hormone replacement therapies are alike estrogen-only therapy may protect against breast cancer.

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Amanda Chan
Amanda Chan was a staff writer for Live Science Health. She holds a bachelor's degree in journalism and mass communication from the Walter Cronkite School of Journalism and Mass Communication at Arizona State University, and a master's degree in journalism from Columbia University.