NEW YORK (Reuters Health) - After menopause, a woman's natural levels of "sex hormones" such as estrogen and testosterone are "strongly associated" with her breast cancer risk, UK researchers report.

"We've known for some time that reproductive and hormonal factors were involved in the development of breast cancer," study leader Dr. Timothy J. Key of the University of Oxford said in a prepared statement from Cancer Research UK. "But until now, we haven't had strong evidence for a direct link between the blood levels of natural hormones and risk of the disease. Our study confirms that high levels of sex hormones can raise risk."

Key and his colleagues reanalyzed nine studies on the topic. Their findings are published in the April 17th issue of the Journal of the National Cancer Institute.

The analysis included a total of 1,765 healthy women and 663 women with breast cancer, none of whom were taking hormone supplements when their blood was analyzed.

Levels of nine different types of sex hormones, including several forms of estrogen, androstenedione, dehydroepiandrosterone sulfate and testosterone, were measured. Risk of breast cancer rose as levels of each of the hormones measured increased.

Women were divided into five groups based on their level of each hormone. Those in the highest group, or quintile, had a breast cancer risk ranging from roughly 50% higher to nearly three times higher compared with those in the lowest quintile, depending on the hormone.

High levels of sex-hormone binding globulin, a protein that reduces the activity of sex hormones, were associated with a decreased risk for developing breast cancer.

Measuring levels of these types of hormones in the future might identify women who face an increased risk of breast cancer, Key and colleagues conclude.

SOURCE: Journal of the National Cancer Institute 2002;94:606-616.

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