An advisory panel to the U.S. National Toxicology Program has recommen Toxicity Panel Recommends Adding Estrogen to Carcinogen List: Cautions Women Not to Worry, but Stay Informed (dateline December 27, 2000) | Breast Health News | Imaginis - The Women's Health & Wellness Resource Network

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Toxicity Panel Recommends Adding Estrogen to Carcinogen List: Cautions Women Not to Worry, but Stay Informed (dateline December 27, 2000)


An advisory panel to the U.S. National Toxicology Program has recommended that the female hormone estrogen be added to the federal list of cancer-causing agents. The panel’s recommendation comes after careful study of estrogen’s role in increasing the risk of endometrial cancer (cancer of the uterine lining), and to a lesser extent, the risk of breast cancer.  However, the physicians who advised the panel members say that women should not be frightened by the panel’s recommendation, but instead, this should encourage women and their physicians to discuss the benefits and risks of taking hormone replacement therapy (HRT), based on their individual medical situation.

It is estimated that 16 million women currently use HRT to help relieve symptoms of menopause (such as hot flashes, vaginal dryness, and sleep disturbances) and to prevent and treat osteoporosis, a degenerative bone disease. Estrogen and progestin (a synthetic form of progesterone) are the two hormone supplements most often used in HRT. Unopposed estrogen (estrogen alone) has been shown to be the most beneficial medication to prevent heart disease in women. However, taking estrogen without progestin to balance the hormonal cycle may cause over-stimulation of the tissue lining the uterus (the endometrium). Uncontrolled tissue growth (hyperplasia) may lead to endometrial cancer. Progestin helps counteracts this risk. Therefore, many physicians prescribe HRT regimens that contain both estrogen and progestin.

According to Susan Wysocki, RN, a nurse practitioner and a member of the National Toxicology Program’s advisory panel, associating estrogen with cancer should not frighten women. Instead, the listing should encourage women to learn how estrogen may be given safely, said Wysocki. Toxicologist Michelle Medinsky told the advisory panel that physicians openly discuss the benefits of HRT with their patients but rarely discuss the risks. Listing estrogen as a carcinogen will help increase patient-physician discussion.

While the link between unopposed estrogen and endometrial cancer risk is well known among the medical community, the link between HRT and breast cancer risk is more controversial. Some studies have shown the risk of breast cancer to be minimal among women who use HRT while other studies have shown a more significant 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, there has been very little research on the use of HRT for a period greater than 20 years.

Women’s health experts blame the media for emphasizing the negative findings of HRT studies while devoting little attention to studies that do not find a relationship between HRT and breast cancer risk. Two large studies conducted by the American Cancer Society and the Iowa’s Women’s Health Study did not find an increased breast cancer risk with HRT, but these studies were not well reported to the public. A 15-year clinical trial is currently underway to investigate HRT, heart disease, osteoporosis, breast cancer, and colon cancer in 63,000 American women between the ages of 50 and 79.

Until more is known about the correlation between HRT and breast cancer risk, the decision to take HRT should be made carefully with a physician, taking into account the women’s medical situation and family history. Many women find that the benefits of taking HRT to help relieve menopausal symptoms outweigh the potential risks of cancer.

Millions of women also take oral contraceptives, which contain estrogen, although most versions of oral contraceptives prescribed today contain low doses of estrogen (50% to 100% less estrogen than most birth control pills contained before 1975). Oral contraceptives used today are not associated with increased breast cancer risk, although one recent study found that women with a strong family history of breast cancer (typically more than five members with breast cancer) who took oral contraceptives before 1975 may have an increased risk of breast cancer.

According to an editorial by Wylie Burke, MD, PhD, ""the use of oral contraceptives needs to be considered on an individual basis, taking into account baseline risk for breast and ovarian cancer, alternative strategies for cancer risk reduction, and other benefits oral contraceptives may provide." Several studies have shown that oral contraceptives significantly reduce the risk of ovarian cancer, especially if taken for more than five years. Because there may be no obvious symptoms associated with early stages of ovarian cancer, many cases are diagnosed in advanced stages, when the chances for survival are much lower.

The National Toxicity Program advisory panel provides advice to the National Toxicity Program, a branch of the National Institutes of Health (NIH). Every two years, the NIH updates the federal list of cancer-causing agents. The National Toxicity Program does not have to follow the advice of its advisory panel, but it usually does so. The next scheduled update of the national carcinogen list will occur in early 2002.

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