A new study conducted by researchers at the National Cancer Institutes shows that women who take combined New Study Links Hormone Replacement Therapy To Breast Cancer Risk (dateline January 31, 2000) | Breast Health News | Imaginis - The Women's Health & Wellness Resource Network

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New Study Links Hormone Replacement Therapy To Breast Cancer Risk (dateline January 31, 2000)

A new study conducted by researchers at the National Cancer Institutes shows that women who take combined hormone replacement therapy —estrogen and progesterone— for more than five years may be at greater risk of developing breast cancer than women who take estrogen alone. Hormone replacement therapy (HRT) is commonly prescribed for post-menopausal women to decrease the frequency of menopausal symptoms (hot flashes, insomnia, and vaginal dryness). HRT has also been shown to decrease the risk of heart disease , osteoporosis, and delay the onset of Alzheimer’s disease .   Physicians are not discouraging women from using HRT, but the results of the study suggest that women on HRT (or those considering HRT) who have a strong family history of breast cancer may wish to carefully evaluate long-term HRT use.

In the study, researchers analyzed data from 46,355 women in the Breast Cancer Detection Demonstration Project, a national breast cancer screening program. The data compared the risk of breast cancer among women who did not take HRT, those who took estrogen alone, and those who took a combination of estrogen and progesterone (progestin) from 1980 to 1995. The results of the study revealed that a woman’s risk of breast cancer increases by only 1% each year if she uses estrogen alone (called estrogen replacement therapy), but her risk increases by 8% each year if she uses estrogen and progesterone (HRT).

A simple way to understand the statistics of this study is to consider a group of 100,000 women who are at a normal weight. The study showed that normal weight women may be at a higher risk of breast cancer when using HRT; however, since the number of overweight women in the study was low, researchers were unable to accurately assess the risk of weight. Among 100,000 normal weight women between the ages of 60 and 64 who do not take HRT, 350 will develop breast cancer within five years. However, if all of the women take HRT for five years, 560 will develop breast cancer. The use of estrogen and progesterone after menopause may stimulate the growth of very small, previously unnoticeable tumors that already exist within the breast, according to Dr. Catherine Schairer of the National Cancer Institute.

Medical experts are quick to point out that the results of this latest study do not conclusively show that HRT increases the risk of breast cancer. The majority of studies have shown that HRT does not significantly increase a woman’s risk for breast disease. According to Trudy Bush, MD, a physician from the University of Maryland School of Medicine, women on HRT should not be alarmed about the results of this study. If women use HRT, they should continue, said Dr. Bush.

Combined HRT (estrogen and progesterone) has only 25% of the hormones compared with oral contraceptives, which have not been shown to increase breast cancer risk. Additionally, if a woman becomes pregnant, she is exposed to estrogen levels that are approximately 100 times more potent than standard HRT, said Dr. Bush.

Taking estrogen pills benefits millions of women by alleviating hot flashes, insomnia, vaginal dryness, and other symptoms that can occur when their ovaries stop producing the hormone, estrogen, at menopause. However, estrogen has also been shown to increase a woman’s risk of cancer of the endometrium—the lining of the uterus. Since the hormone, progesterone, counteracts this risk, women who have not had their uteruses removed are often prescribed combined HRT (progesterone and estrogen). It is estimated that 8.6 million American women take both estrogen and progesterone according to Wyeth-Ayerst Laboratories, a drug company that makes Premarin, a type of synthetic estrogen. Another 12 million women who have had hysterectomies (removal of the uterus) take estrogen alone.

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