According to a new study, women who gain weight in adulthood face a higher lifetime risk of all types of breast cancer even if they do not take hormone replacement therapy after menopause.
Published in the July 1, 2006 issue of CANCER, a peer-reviewed journal of the American Cancer Society, the study reveals that the greater the weight gain as an adult, the greater the risk for all histological types, tumor stages, and grades of breast cancer, particularly advanced malignancies. The most extremely obese women were up to three times more likely to have regional or distant metastases than women with less weight gain. The study is the first to investigate the relationship between weight gain and type of breast cancer.
Breast cancer risk is linked to increased lifetime levels of circulating estrogen. Fat tissue increases circulating estrogen, thereby adding to the risk. Previous studies have shown, though, that the risk can be affected by other factors. Postmenopausal women who take hormone replacement therapy actually mitigate the effects of obesity on cancer risk. Moreover, current weight as defined by body mass index is not as important as a woman's weight gain from the age of 18.
While there is much literature on the risk of obesity and breast cancer, there is no data on whether that risk is specific for the type of breast cancer. Led by Heather Spencer Feigelson, Ph.D., M.P.H of the American Cancer Society, researchers investigated the risk between weight gain and type of invasive breast cancer among 44,161 postmenopausal women who were not taking hormone therapy.