Shieh Y, et al. - In this case-control study nested within two mammography screening cohorts, researchers examined the link between breast density and estrogen receptor (ER) subtype according to body mass index (BMI) and menopausal status. In pooled analysis, there were 1,538 ER-positive and 285 ER-negative invasive breast cancer patients, as well as 4,720 controls who were matched on age, menopausal status at time of mammogram, and year of mammogram. A higher risk of ER-negative vs ER-positive cancer was observed in relation to the combination of overweight/obesity and elevated breast density in premenopausal women. In the United States, high BMI and breast density is present in 18% of premenopausal women; lifestyle modifications, including weight loss and exercise, may be beneficial for these women.