Waist circumference and risk of breast cancer in Korean women: A nationwide cohort study.

Although postmenopausal breast cancer (BC) risk has been linked to adiposity, associations between adiposity and premenopausal BC remain unclear. To address this question, we investigated the association of BC risk with measures of adiposity, including body mass index (BMI) and waist circumference (WC), in a large cohort of Asian women. We used a nationwide cohort of adult Korean women selected from the National Health Insurance Corporation database merged with national health examination data from 2009 to 2015. A total of 11,227,948 women were tracked to retrospectively identify incident cases of BC. Our analysis used Cox proportional hazards models to calculate hazard ratios and assess the association of BC risk with BMI and/or WC in both pre- and postmenopausal women. BMI and WC were robustly associated with increased risk for postmenopausal BC (ptrend <0.001 for both BMI and WC) but not with premenopausal BC. Association between WC and premenopausal BC was only statistically significant when considering BMI (ptrend =0.044). In contrast, postmenopausal BC was negatively associated with WC when considering BMI (ptrend =0.011). In premenopausal women, WC may predict increased BC risk when considering BMI. However, in postmenopausal women, WC is not superior to BMI as an indicator of BC risk.