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 Pittsburghs 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 womans 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 Womens Health
Trial, have shown that dietary modifications can reduce blood levels
of estradiol in postmenopausal women. In another study by the
Womens 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.