Abstract LB-285: Obesity and breast cancer subtypes in African American women participating in the AMBER Consortium

Abstract

Abstract Introduction. Obesity has been shown to be associated with reduced risk in premenopausal women and increased risk in postmenopausal women, with evidence coming largely from studies in white women. African American (AA) women are more likely than white women to be obese and to have central obesity (measured as a high waist to hip ratio (WHR) or waist circumference). They are also more likely to be diagnosed with ER- and triple negative (TN) breast cancers, which tend to have poorer prognosis than ER+ tumors. There is growing evidence that risk profiles for these subtypes may differ. However, few studies have evaluated the impact of general and central obesity on breast cancer subtypes in AA women. Methods. We pooled data from three studies in AA women, the Black Women Health Study, the Carolina Breast Cancer Study, and the Women's Circle of Health Study, to evaluate the association of recent body mass index (BMI), young adult BMI (at age 18-21 y), and waist to hip ratio (WHR) with breast cancer subtypes. Cases were categorized according to hormone receptor subtype as ER+, ER-, and triple negative (TN: ER-, PR-, and HER2-) based on pathology reports or cancer registry data. A total of 1,809 ER+ cases, 1,024 ER- cases (which included 478 TN cases), and 9,593 controls were included in the analyses. Odds ratios (OR) and 95% confidence intervals (CI) were computed using unconditional polytomous or regular logistic regression, as appropriate, taking into account all major risk factors for breast cancer. Results. Recent BMI was inversely associated with postmenopausal ER- breast cancer (OR: 0.74; 95% CI: 0.53-1.02), and more strongly with tumors that were also PR- and HER2- (TN), (OR: 0.61; 95% CI: 0.39-0.97 for BMI≥35 vs. <25). For ER+, ORs were below one for pre-menopausal and above one for post-menopausal breast cancer, but confidence intervals included 1.0. However, among women who were thin as young adults (BMI<19.4, lowest tertile), recent high BMI (≥35) was associated with more than a twofold increase in risk of postmenopausal ER+ breast cancer (OR: 2.24; 95% CI 1.46-3.43, p for interaction: 0.02). Associations between recent BMI and ER- breast cancer did not differ by young-adult BMI. There was a suggestion of increased risk for high WHR (highest vs. lowest quartile) independent of BMI, which only approached statistical significance for premenopausal ER+ tumors (OR: 1.31; 95% CI: 0.98-1.75; p for trend: 0.05). In analyses of the joint effects of recent BMI and WHR, the association of WHR with ER+ tumors in postmenopausal women was strongest for women with normal BMI (OR: 1.61; 95% CI: 1.02-2.56), p for interaction: 0.05. Conclusion. Our results indicate the need to consider subtypes when evaluating the impact of general and central obesity on breast cancer and warrant the study of mechanisms underlying these complex associations. Citation Format: Elisa V. Bandera, Urmila Chandran, Chi-Chen Hong, Christine B. Ambrosone, Melissa Troester, Kathryn L. Lunetta, Lucile Adams-Campbell, Andrew Olshan, Julie R. Palmer, Lynn Rosenberg. Obesity and breast cancer subtypes in African American women participating in the AMBER Consortium. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-285. doi:10.1158/1538-7445.AM2014-LB-285