ESR1 and breast cancer: We previously reported that women in the larger, baseline National Institutes of Health (NIH)-AARP (formerly the "American Association of Retired Persons") Diet and Health Study cohort who were physically active five or more times per week during the year prior to baseline questionnaire administration showed a 13% reduced risk of postmenopausal breast cancer, with suggested heterogeneity in the association according to tumor estrogen receptor (ER) status and lifestyle and reproductive factors [24].