Higher amounts of the pregnancy hormones estradiol and progesterone were associated with a greater risk of hormone receptor (HR)-negative breast cancer before age 50 years, according to a study by German researchers. The nested, casecontrol study was presented at the American Association for Cancer Research (AACR) International Conference on Frontiers in Cancer Prevention Research held in October 2012. Investigators assessed the effects of hormone exposure during early pregnancy and its possible effect on maternal breast cancer.
Annekatrin Lukanova, MD, PhD, associate professor at the German Cancer Research Center in Heidelberg, says that the association between pregnancy and breast cancer risk is complex and that researchers do not fully understand the biological mechanisms for the protective effect of childbearing on cancer risk. She and colleagues used the Northern Sweden Maternity cohort to conduct the study, which compared 417 controls with 223 women who had donated blood samples during their first trimester of pregnancy and who later developed breast cancer. About three-quarters of the women with diagnosed cancer had HR-positive cancer.
The 2 groups of hormones that researchers examined were: estradiol, estrone, and progesterone, which increase substantially with pregnancy progression; and testosterone and insulin growth factor-1 (IGF-1). Researchers found that circulating concentrations of IGF-1 are directly associated with risk for HRpositive breast cancer, which is in line with studies of women who were not pregnant. At the same time, they found a higher risk of HR-negative breast cancer diagnosed before age 50 years affiliated with higher levels of estradiol and progesterone.
Because the study was small and the hormones were only measured during the first trimester of pregnancy, further and larger studies are needed to better understand the association of pregnancy hormones with the risk for hormone-defined maternal breast cancer, says Dr. Lukanova.