UC Davis

PURPOSE: The incidence of triple-negative breast cancer (TNBC) is higher in Black women compared to White women which is not explained by racial differences in body mass index (BMI). As BMI has limitations as an anthropometric measure, we used different anthropometric measures to examine associations with TNBC by race. METHOD: Of 161,808 postmenopausal participants in Womens Health Initiative, eligible were a subsample of 121,744 White and Black postmenopausal women enrolled from 1993 to 1998, 50-79 years of age with anthropometric measures who were followed for breast cancer incidence until March 2019. At entry, BMI, waist circumference (WC), and waist-hip ratio (WHR) were measured using standardized methods. Breast cancers were verified by central medical record review. Associations between anthropometric measures and triple-negative breast cancer risk were examined using Cox proportional hazards regression models. RESULTS: After 17.6 years (median) follow-up, there were 87 Black women and 529 White women with incident triple-negative breast cancer. Overall, there were no significant associations between anthropometric measures and risk of triple-negative breast cancer. However, compared to White women with normal BMI, White women with obesity (BMI ≥ 30) (HR 0.76, 95% CI 0.60, 0.96) were significantly associated with a lower risk of triple-negative breast cancer. And larger waist circumference (HR per centimeter 0.99, 95% CI 0.99, 1.00) was significantly associated with a lower risk of triple-negative breast cancer among White women. CONCLUSION: Overall, among postmenopausal women, anthropometric measures were not associated with risk of TNBC. The association among White women with larger waist circumference and women with obesity with a lower risk of triple-negative breast cancer needs further confirmation.