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U.S. National Cancer Institute to Investigate Link Between Early-Reproductive Hormonal Factors and Breast Cancer (dateline May 27, 2003)

The U.S. National Cancer Institute has announced that it will hold a workshop entitled, "Early Reproductive Events and Breast Cancer Risk," in early 2003 to address hormonal factors that may protect or increase a woman’s risk of developing breast cancer. The announcement comes as extensive research has focused on hormonal exposures and their link with breast cancer. The meeting will enable the National Cancer Institute to prioritize funding of and the administration of these studies. Ultimately, the goal is for experts to better understand how hormones can influence breast cancer risk.

Early-reproductive events, such as full-term pregnancy before age 30, have been shown to protect women against the development of breast cancer later in life while other hormonal events, such as the early onset of menstruation (before at 12) or late menopause (after age 50) have been shown to increase breast cancer risk.

Pregnancy seems to decrease the risk of breast cancer if a woman becomes pregnant with her first child before age 30. This is due to an interruption of menstrual cycles during pregnancy. Women who never become pregnant are at a higher risk of breast cancer than those who have a first child before age 30. However, pregnancy after age 30 appears to also increase the risk of breast cancer. The older a woman is, the more likely her breast tissue has already been exposed to some cancer-causing substances (carcinogens). Therefore, exposure to elevated hormone levels during pregnancy at a later age may stimulate the growth of abnormal breast tissue. In fact, some experts believe that the number of menstrual cycles that occur between a woman’s first period and her first pregnancy is a greater predictor of breast cancer risk than her age at her first menstruation or menopause. The National Cancer Institute meeting is designed to address these issues and to identify ways to better understand how hormonal factors influence the risk of breast cancer.

Because estrogen has been linked to breast cancer risk, there have also been a number of studies that have investigated whether menopausal hormone replacement therapy (HRT) increases a woman’s risk of developing breast cancer. To date, emerging evidence is showing that long-term use of HRT does increase the risk of developing post-menopausal breast cancer, though the risk still appears to be small (of 10,000 women taking HRT, eight more will develop breast cancer each year, compared with non-HRT users).

Another area of research that the National Cancer Institute workshop will address is the association between breast cancer risk and abortion. While several studies over the past two decades have explored the possible connection between abortion and breast cancer risk, the results have been contradictory. Some studies have shown a small increase in the risk of breast cancer in women with a history of abortions while other studies have found no such risk. Even some studies that have shown that a history of abortions can increase a woman’s risk for breast cancer have been criticized because factors in these studies (such as reporting bias) may have contributed to inaccurate results.

The National Cancer Institute workshop will focus on studies that define risk factors for breast cancer and the underlying biology of these risk factors. According to the National Cancer Institute, "scientists and clinicians participating in the workshop will seek to identify the gaps in our knowledge of reproductive risk factors, including those associated with spontaneous and induced abortion, and suggest new opportunities for interdisciplinary studies that would fill these gaps."

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