Abstract C072: Maximum body mass index and breast cancer incidence in Black women

Abstract

Abstract Introduction: The prevalence of obesity is high in African American (AA) women. Excess weight is an established risk factor for postmenopausal breast cancer (and inversely associated with premenopausal breast cancer), but studies of recent body mass index (BMI) in AA women have shown relatively modest associations. The use of maximum BMI attained during adulthood, which is less likely to be influenced by recent illness, has been suggested as an alternative exposure metric and has yielded stronger associations for some outcomes. Whether maximum BMI attained during adulthood is associated with risk of breast cancer has not yet been evaluated. Methods: We evaluated associations of maximum BMI attained during follow-up with incidence of all breast cancer and with breast cancer subtypes in 56,919 AA women in the prospective Black Women’s Health Study. From 1995 to 2013, we identified a total of 2708 breast cancers, of which 2008 were invasive cancers, including 1446 estrogen receptor (ER) positive and 652 ER negative. We used multivariable Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for associations by ER status and menopausal status. Results: Compared to a maximum BMI of <25 kg/m², having a maximum BMI of ≥35 kg/m² (Obese II) was associated with increased risk of ER+ (HR=1.29, 95% CI 1.05-1.59) and postmenopausal breast cancer (HR=1.38, 95% CI 1.12-1.70), after adjustment for BMI at age 18 and other breast cancer risk factors. The association of maximum BMI with ER+ breast cancer was observed among postmenopausal women (HR=1.63, 95% CI 1.24-2.15) but not premenopausal women. The associations observed for maximum BMI were stronger in magnitude than associations for recent BMI in the same dataset. Conclusion: A maximum attained BMI of ≥35 kg/m² is associated with substantially increased risk of ER+ breast cancer among postmenopausal AA women. These findings provide new insights into the impact of obesity on breast cancer risk in this population, and suggest that maximum BMI may be a useful metric for understanding associations between adiposity and breast cancer risk. Citation Format: Wambui G. Gathirua-Mwangi, Julie R. Palmer, Victoria Champion, Lucile L. Adams-Campbell, Andrew Marley, Michele Forman, Lynn Rosenberg, Kimberly A. Bertrand. Maximum body mass index and breast cancer incidence in Black women [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr C072.