Obesity Linked to All Types Breast Cancer

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. To be published in the July 1, 2006, issue of CANCER, the study reveals that the greater the weight gain as an adult, the greater the risk for all histologic 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.

Study Specifics

While there is much literature on the risk of obesity and breast cancer, no data indicate whether that risk is specific for the type of breast cancer. Led by Heather Spencer Feigelson, PHD, mph, 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.

The researchers found that the greater the weight gain, the greater the risk for all types, stages, and grades of breast cancer. Compared to women who gained 20 lb or less during adulthood, women who gained over 60 lb were almost twice as likely to have ductal-type tumors and more than 1.5 times more likely to have lobular-type cancers. The risk for metastatic disease increased for all women who gained weight, with the risk greater than threefold for women who gained over 60 lb. As expected, weight gain increased the risk of estrogen receptor-positive tumors, but not of tumors that did not present estrogen receptors.

Dr. Feigelson and her colleagues conclude that "these data further illustrate the relationship between adult weight gain and breast cancer, and the importance of maintaining a healthy body weight throughout adulthood."