Higher levels of certain sex hormones are shown to be associated with a higher risk of breast cancer in premenopausal women, according to an analysis that pooled seven prospective studies of hormones and breast cancer risk. These increased risks associated with higher concentrations of sex hormones in premenopausal women are smaller but qualitatively similar to those previously reported in postmenopausal women, the researchers say.
Higher levels of certain estrogens and other sex hormones are shown to be associated with a higher risk of breast cancer in premenopausal women, according to an analysis from the University of Oxford that pooled seven prospective studies of hormones and breast cancer risk. A doubling of concentrations of those hormones increased the risk of breast cancer by 20% to 30%.
“This study suggests that, just like in older women, one of the major risk factors with breast cancer has to do with lifetime exposure to estrogen,” says Ann Partridge, MD, MPH, director of the program for young women with breast cancer in the Susan F. Smith Center for Women's Cancers at Dana-Farber Cancer Institute in Boston, MA.
Studies have shown that factors contributing to higher levels of estrogen over a woman's lifetime—including beginning menstrual cycles at an earlier age, beginning menopause later, and not having children—pose higher risks of postmenopausal breast cancer. The increased risks associated with higher concentrations of sex hormones in premenopausal women identified in the new analysis are smaller but qualitatively similar to those previously reported in postmenopausal women, the researchers say.
Uncovering this similar link in younger women has been more challenging because only about 20% of breast cancers are diagnosed in women younger than 50. “You have to use a pooled analysis to get enough data,” says Partridge, who was not involved in the analysis.
The study, published in The Lancet Oncology, examined the levels of hormones in blood from 2,466 women under 50 years of age, 767 of whom had breast cancer. Collaborators in the Endogenous Hormones and Breast Cancer Collaborative Group at the Nuffield Department of Population Health at the University of Oxford in Oxford, UK, controlled for fluctuations of the blood hormone levels during the menstrual cycle. Most of the women were of white European descent.
The group found that higher concentrations of estradiol, estrone, androstenedione, dehydroepiandrosterone sulfate, and testosterone were associated with increased breast cancer risk.
Lead author Timothy Key, PhD, notes that because hormone levels fluctuate widely during the menstrual cycles of younger women, these findings cannot be used to classify the breast cancer risk for individual women.
Even for older women, hormone levels generally are not used as part of the risk assessment process. “It's a fairly robust predictor, but it's not clear it adds information that will change a woman's decision,” says Partridge. “It's complex. Essentially a lot of estrogen is a carcinogen. But figuring out which particular person is at high risk and how to prevent cancer in them is the future.”