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Estrogen-Only Hormone Replacement Therapy Seems to Decrease Risk

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Much research has shown a link between higher breast cancer risk and using HRT (hormone replacement therapy) to treat menopausal symptoms. The results aren't exactly the same, but there is good evidence that:

  • HRT increases the risk of invasive breast cancer.
  • Breast cancer risk goes up in the first several years of HRT use; risk seems to keep increasing the longer a woman uses HRT.
  • Both combination HRT (contains both estrogen and progesterone) and estrogen-only HRT increase breast cancer risk, but combination HRT increases risk more.
  • High-dose HRT increases risk more than low-dose HRT.

A new study has different results: postmenopausal women who took estrogen-only HRT had a somewhat lower risk of invasive breast cancer, both while using HRT and after stopping HRT, compared to postmenopausal women who took a placebo (sugar pill).

Still, the risks of other serious health problems -- including blood clots in the legs (deep vein thrombosis or DVT), blood clots in the lungs (pulmonary embolism), and stroke -- were higher when women used estrogen-only HRT.

The research is published in the Journal of the American Medical Association.

The Estrogen-Alone Trial was part of the larger Women's Health Initiative (WHI) study. Nearly 11,000 postmenopausal women, age 50 to 79, participated in the Estrogen-Alone Trial. All the women had had a hysterectomy (surgery to remove the uterus) when they started this trial. Half the women took estrogen-only HRT and the other half took a placebo (sugar pill) that looked just like the HRT pill. Neither the women nor the doctors knew which women were taking HRT and which women were taking the placebo.

After the study started, the women could stop treatment whenever they wanted. On average, the women took HRT or the placebo for fewer than 6 years. Though they didn't stop treatment entirely, many women took fewer doses than prescribed. Overall, the women took all or nearly all of the prescribed treatment for about 3.5 years.

After about 7 years of follow-up, the researchers looked at the women's health histories. They found that compared to women who took the placebo, women taking estrogen-only HRT had a higher risk of some serious health problems, though these problems didn't happen very often:

  • blood clots in the leg (DVT) were 47% more likely
  • blood clots in the lung were 37% more likely
  • stroke was 36% more likely

Women age 60 or older had the highest increase in risk for these serious health problems.

The researchers also found that the risk of invasive breast cancer was 21% lower in women taking estrogen-only HRT compared to women taking the placebo.

Because of the increase in risk for serious health problems in women taking estrogen-only HRT, the study was stopped. Still, 7,645 of the women agreed to be part of longer follow-up and were followed for more than 11 years after they first started the study.

Using this long-term information, the researchers found that in the years AFTER the study (and HRT or placebo) stopped, the risk of serious health problems in women who took estrogen-only HRT during the study was now the same as the risk in women who took the placebo. This risk was higher DURING the study, which means that stopping the estrogen-only HRT took away the increase in risk.

After 11 years, the researchers also found that the risk of invasive breast cancer was still 25% lower in women who took estrogen-only HRT when the study was active compared to women who took the placebo.

Menopausal side effects can dramatically reduce quality of life for some women. These women have to weigh the benefits of HRT against the risks. If you're having severe hot flashes or other menopausal side effects and are considering HRT, talk to your doctor about all of your options. Ask how you can minimize your breast cancer risk AND relieve your symptoms. Be sure to discuss the pros and cons of different types and doses of HRT.

Almost all other research suggests that estrogen-only HRT increases invasive breast cancer risk less than combination HRT. This study suggests that invasive breast cancer risk may actually go down with estrogen-only HRT. Still, other serious health risks went up substantially when women took estrogen-only HRT. It's reassuring that those risks went down after HRT was stopped.

If you do decide to take HRT try to take it for the shortest time possible. You also may want to ask about vaginal or transdermal HRT.

Learn more about menopause and ways to manage side effects on the Breastcancer.org Managing Menopausal Symptoms pages.

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