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Birth Size Linked to Early Breast Cancer

Estrogen Exposure In Utero Could Be the Cause
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Jan. 30, 2003 -- Your size at birth could predict your risk of premenopausal breast cancer. Exposure to excess estrogen during fetal development may be to blame, experts say.

In a new study, researchers analyze health records for more than 5,000 Swedish women, looking for links between fetal growth and risk of breast cancer. It's an association that several studies have identified.

Researchers in this current study found "strong evidence" of a link between large birth size and risk of premenopausal breast cancer, writes Valerie McCormick, an epidemiologist with the London School of Hygiene and Tropical Medicine. Her study appears in this month's British Medical Journal.

It focuses on 5,358 women, all born between 1915 and 1929 -- average age of 62. Researchers found 63 cases of breast cancer in women when they were younger than 50 years old. These women had, on average, a larger birth size in terms of length and head size, and they were born prematurely, reports McCormick. The rates of premenopausal breast cancer in these women were three to four times that found in women who were smaller in size at birth.

This finding lends support to a popular theory -- that during development of a fetus' breast tissue exposure to high concentrations of estrogen affects risk of breast cancer.

Breast development in the fetal stage may be vulnerable to assaults from excess estrogen circulating in the mother's bloodstream, says McCormick.

However, large birth size is likely responsible for only a small proportion of breast cancer cases because the rates of premenopausal breast cancer are low, McCormick says.

SOURCE: British Medical Journal, Jan. 25, 2003.

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