Sex Hormone Levels May Help Predict Breast Cancer Risk

Results of a study published in a recent issue of the Annals of Internal Medicine suggest that, in the near future, a simple blood test that detects levels of sex hormones could predict which women are at highest risk of developing breast cancer. Armed with this information, physicians could determine who would be good candidates for drugs that can reduce the risk of the disease. Jane A. Cauley, DrPH, associate professor of epidemiology at the University of Pittsburgh’s Graduate School of Public Health, led the multicenter, federally funded study.

“In our study of older women, we found that those with the highest levels of either serum estradiol or testosterone were three times more likely than expected to develop breast cancer,” said Dr. Cauley. “This magnitude of risk is much higher than that observed for other breast cancer risk factors.”

“Each year more than 180,000 women are diagnosed with breast cancer in the United States. Although well-established risk factors exist for breast cancer, more than 90% of all women have at least one of these factors and, individually, each factor only modestly increases a woman’s risk of developing the disease,” she said.

Hormone Levels and Breast Cancer Incidence

The research involved participants from the Study of Osteoporotic Fractures and included 97 women who developed breast cancer and 244 randomly selected controls. All of the women were white, 65 years of age or older, and not receiving estrogen. The estimated incidence of breast cancer was lowest (4 case per 10,000 women per year) in women with the lowest blood levels of estradiol and testosterone. Conversely, the incidence of breast cancer was highest (65 cases per 10,000 women per year) in women with the highest concentrations of both those hormones.

According to Dr. Cauley, this research supports previous reports indicating that hormone levels influence the risk of breast cancer. “This type of information could help clinicians direct high-risk women to consider chemoprevention for breast cancer,” said Dr. Cauley. “Results from the Breast Cancer Prevention Trial and the Multiple Outcomes of Raloxifene Evaluation Trial have shown that certain medications can reduce the incidence of breast cancer.”

Unlike previous reports, results of this study determined that testosterone and estradiol independently contributed to breast cancer risk. For many years, researchers have known that estradiol, a metabolic product of estrogen, fuels the growth of some breast cancers; however, the way that testosterone contributes to breast cancer growth is still unclear, said Dr. Cauley.

Modifications to Reduce Hormone Levels

Studies are currently underway to determine whether selective estrogen receptor modifiers (SERMs) can reduce the incidence of breast cancer in women who have high baseline measurements of estradiol. In addition, studies, such as the Women’s Health Trial, have shown that dietary modifications can reduce blood levels of estradiol in postmenopausal women. In another study by the Women’s Health Initiative, investigators are assessing whether reduced dietary fat will translate into a decrease in the number of breast cancer cases.

Because absolute levels of hormones are low in older women, the study employed extremely sensitive, accurate assays to measure differences in levels among study participants. These sensitive assays are not yet clinically available, said Dr. Cauley.