Combined Hormone Therapy at Menopause Leads to Higher Breast Cancer Risk

First Posted: Mar 30, 2013 09:51 AM EDT

Hormone therapies that include estrogen and progestin could increase the risk of breast cancer for women. A new study reveals that women who started taking these therapies just as menopause began were far more likely to develop disease.

The new research, published online in the Journal of the National Cancer Institute, was a longer-term analysis of data from the observational Women's Health Initiative (WHI). Following nearly 42,000 women past menopause for about 11.3 years, the researchers examined the likelihood of the women developing breast cancer after starting hormone therapies. About 25,000 women in the study did not use hormone therapy while 16,000 took a combined dose of estrogen and progestin. The researchers did not include estrogen-only therapy in their study.

More than 2,200 women developed breast cancer by the end of the study. But the difference between hormone users and non-hormone users was certainly not equal. The scientists found that the breast cancer risk for hormone users was a whopping .60 percent compared with the .42 percent among non-hormone users. In addition, they found that women who began hormone therapy right at the time of menopause had an even greater risk of developing breast cancer.

While this particular link between breast cancer and hormone therapy has been found in other studies, this is the first one that found a greater risk for women who began using hormone therapy earlier.

"We had a substantial number closer to menopause than the clinical trial of [The Women's Health Initiative]," said Rowan Chlebowski, lead researcher of the study, in an interview with Health Day.

It's possible that women who start the hormone therapy closer to menopause still have circulating levels of estrogen that are high enough to make them exceed some sort of threshold. Beyond this threshold, the hormones could be hazardous to their health.

The new study could lead to new dosages for women who are attempting to combat the effects of menopause with hormone therapy. In addition, the analysis reinforces previous findings that combination hormone therapy is linked with breast cancer risk. It could also make women think twice before starting a course of treatment, weighing whether their current symptoms are worth the risk.

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