Eating Disorders and Breast Cancer.

BACKGROUND: Eating disorders such as anorexia nervosa and bulimia nervosa affect overall and reproductive health and may also affect breast cancer risk. We studied the association between self-reported eating disorders and breast cancer risk in a prospective cohort study. METHODS: In 2003-2009, the Sister Study enrolled women ages 35-74 years who had a sister with breast cancer but had never had it themselves. Using data from 47,813 women, we estimated adjusted HRs and 95% confidence intervals (CI) for the association between eating disorders and invasive breast cancer over a median of 5.4 years of follow-up. RESULTS: Three percent (n = 1,569) of participants reported a history of an eating disorder. Compared with women who never had an eating disorder, women who reported eating disorders in the past had reduced breast cancer risk (HR = 0.62; 95% CI, 0.42-0.92). CONCLUSIONS: In this large prospective, observational cohort study, we observed an inverse association between having a history of an eating disorder and invasive breast cancer. IMPACT: Historical eating disorders may be associated with a long-term reduction in breast cancer risk. Cancer Epidemiol Biomarkers Prev; 26(2); 206-11. ©2016 AACR.