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Hormone Replacement Therapy (HRT) Increases Breast Density, Density Decreases After HRT is Discontinued (dateline January 17, 2001)

The results of a newly published study confirm previous findings which show that the use of hormone replacement therapy (HRT) can increase breast density in some women, making breast cancer more difficult to detect with screening mammography. However, the researchers also found that breast density usually decreases again after HRT is discontinued. According to Carolyn M. Rutter, PhD and her colleagues, the study provides important new information that women and their physicians should consider when beginning or discontinuing HRT. The study also reinforces the belief that women on HRT should be closely monitored by physicians with regular physical breast exams in addition to annual mammograms and monthly breast self-exams.  

The large Seattle study involved 5,212 post-menopausal women, each of whom received two screening mammograms between 1996 and 1998. After analyzing the women’s mammograms, the researchers found that women who used HRT since entering the study were approximately two and a half times more likely to have increased breast density than non-HRT users. However, the researchers also found that women who discontinued HRT were more likely to show decreases in breast density and women who continued taking HRT were more likely to show increases in density and sustained high density.

"This result has important implications for breast cancer screening," wrote Dr. Rutter and her colleagues. Breast density (glandular tissue) appears as white areas on a mammogram film and can make it more difficult to detect microcalcifications (calcium deposits) and other masses, since breast abnormalities also show up as white areas on a mammogram film. After menopause, the glandular tissue of the breasts is replaced with fat, typically making abnormalities easier to detect with mammography. However, it appears as though HRT can temporarily increase breast density again, which can interfere with mammogram interpretation.

However, researcher Stephen Taplin, MD of the Group Health Cooperative in Seattle, also called the study reassuring because breast density decreases after HRT use is discontinued. The researchers do not recommend that women repeatedly start and stop taking HRT in hopes of decreasing breast density. Instead, women who take HRT should be closely monitored by physicians and may wish to consider alternatives to HRT if the therapy is interfering with breast cancer detection. All women 40 years of age and older should receive annual mammograms to help detect breast cancer in its earliest stages

HRT is the most commonly prescribed therapy to help ease menopausal symptoms, such as hot flashes and vaginal dryness. HRT also helps prevent and treat osteoporosis, a degenerative bone disease, and studies are investigating whether HRT is beneficial for heart disease, Alzheimer’s disease, diabetes, and other conditions. HRT regimens consist of estrogen, progestin (a synthetic form of the hormone, progesterone), or a combination of the two hormones.

According to Dr. Rutter and her colleagues, their study raises another issue that women and physicians should discuss when considering HRT. Some research has also suggested a link between HRT and increased breast cancer risk. Although studies have been inconsistent, there appears to be an emerging consensus that HRT does not significantly increase the risk for breast cancer, at least for women who take estrogen less than five years or who take less than 0.625 mg per day. However, additional studies are needed to help clarify the risk. Recently, a study conducted by the American Cancer Society found a lower death rate among women who took HRT than non-HRT users. The study also found that HRT may help protect against heart disease in women with low body masses.

Women’s health experts recommend that women discuss the use of HRT carefully with their physicians. HRT is a tradeoff between the proven benefits of relieving menopausal symptoms and preventing diseases such as osteoporosis versus the possibility of increasing breast density or the risk of breast cancer. According to physicians, weighing the benefits and risks of HRT and taking into account individual medical circumstances can help women and their physicians come to an appropriate decision regarding HRT.

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