Does Hormone Therapy Counter the Beneficial Effects of Physical Activity on Breast Cancer Risk in Postmenopausal Women?

Objective—Studies consistently demonstrate that physical activity is inversely associated with postmenopausal breast cancer. Whether this association is stronger among non-hormone users or former users of menopausal hormone therapy (HT) is of interest given the marked decline in HT use since 2002. Methods—The Women’s Contraceptive and Reproductive Experiences Study, a population-based case-control study of invasive breast cancer, recruited white women and black women ages 35–64 years, and collected histories of lifetime recreational physical activity and HT use including estrogen-alone therapy (ET) and estrogen plus progestin therapy (EPT). Results—Among postmenopausal women (1908 cases, 2013 control participants), breast cancer risk declined with increasing levels of lifetime physical activity among never HT users; among short-term HT users (fewer than 5 years); and current ET users; Ptrend values ranged from 0.004 to 0.016. In contrast, physical activity had no significant association with risk among long-term an