How can aerobic exercise lower breast cancer risk?

It's well documented that exercise can decrease the risk of breast cancer, but how? Clinical evidence suggests that changes in estrogen metabolism in premenopausal women may play a part. Mindy Kurzer, director of Consortium member center Healthy Foods, Healthy Lives, was part of a recent study investigating this relationship. Results show that in healthy premenopausal women "an exercise regimen of 150 minutes of moderate-to-vigorous aerobic exercise per week for 16 weeks resulted in significant changes in estrogen metabolism in a direction consistent with reduction of breast cancer risk." Read the paper in Cancer Epidemiology, Biomarkers & Prevention.