Hormone Replacement Therapy Doubles Breast Cancer Risk

Women taking hormone replacement therapy (HRT) for five years or more after menopause double their risk for breast cancer, according to a new study from Stanford University.

Results of this study are based on a follow up to the large-scale Women’s Health Initiative (WHI) study from 2002, which showed that postmenopausal women on estrogen and progestin were at a much greater risk of breast cancer and other serious illnesses than women on placebo. Although women on the combination hormone therapy were advised to stop taking the pills when the results were announced in 2002, they continued to be monitored.

In this new study, researchers analyzed data from two groups of women. The first included more than 15,000 women from the original WHI study of 2002. The second group was composed of nearly 41,500 women enrolled in a separate WHI study that began in 1994, where “real-world women” could choose whether or not to take HRT. About 40 percent of these women chose to take HRT at the beginning of the study and, on average, continued treatment for about seven years.

Researchers found that incidence of breast cancer was very similar in the two groups. In the first WHI study, breast cancer was much more prevalent among the women on HRT than those on the placebo. However, once women stopped the combination therapy, the number of breast cancer diagnoses fell 28 percent within the year.

Women in the observational study were not given direct advice to stop HRT once the 2002 results were known, but many chose to do so on their own. Within a three-year time span, from 2000 to 2003, half of these women chose to stop using HRT, which coincided with a 43 percent decline in breast cancer rates for them from 2002 to 2003. Those who stayed on HRT for at least five years were found to double their risk of breast cancer.

Mammography use did not impact the results, the researchers added. Women in the observational WHI study were encouraged to continue with regular mammograms; use of the screening test remained the same for every woman during the trial. In the large-scale study published in 2002, women did not change how often they went for mammograms.

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specialty: endocrinology