Abstract C097: Association between a healthy lifestyle index and breast cancer risk among post-menopausal women in the Multiethnic Cohort (MEC) Study

Abstract Consistent evidence supports maintaining a healthy weight, engaging in physical activity, and limiting alcohol consumption as potential strategies for reducing breast cancer risk. Sleep duration and sedentary behavior are also emerging breast cancer risk factors. While these cardiometabolic factors have been associated with an increased risk of breast cancer, prior studies have primarily investigated these factors separately. The association between a healthy lifestyle index (HLI) and breast cancer risk, particularly across racially and ethnically diverse postmenopausal women, has not been well studied. Within the Multiethnic Cohort study, ongoing analyses are examining associations between an HLI and risk of invasive breast cancer among 65,813 eligible postmenopausal women (African American [18.7 %], Native Hawaiian [6.7 %], Japanese American [28.2%], Latina [21.1%], and White [25.3%]). During a median follow-up of 23 years, 4,571 incident invasive breast cancer cases were diagnosed between baseline (1993-1996) and the end of follow-up (2017). Self-reported baseline information on seven lifestyle factors was used to create an HLI based on the sum of scores (max HLI score=23): Healthy Eating Index 2010 (HEI 2010) score divided into quartiles (scored 1-4), metabolic equivalents (METs) of moderate and vigorous physical activity (1-3), time spent sedentary (1-3), smoking status and duration (1-5), alcohol consumption (1-3), body mass index (BMI) (1-3) and sleep duration (1-2). Preliminary analyses included descriptive statistics as well as age- and race and ethnicity-adjusted Cox proportional hazards models of invasive breast cancer to estimate hazard ratios (HR) and 95% confidence intervals (CIs) for the association with HLI score (tertiles, (T)) using age as the timescale. The mean HLI score in the overall population was 15.3 [Standard Deviation (SD): 2.1] with 51.4% of the analytic population in an HLI score tertile of ≥18 to 23 (T3; most healthy) and 13.2% in the lowest HLI score tertile ≥7 to <15 (T1; least healthy). The mean HLI scores by race/ethnicity were the following: African American 16.5 [SD: 2.5], Native Hawaiian 16.7 [SD: 2.6], Japanese American 18.2 [SD: 2.2], Latina 17.3 [SD: 2.2] and White 17.2 [SD: 2.6] women. Preliminary findings suggest that overall, women in HLI score T3 had on average, a BMI of 23.6 [3.7] (mean [SD] kg/m2), dietary intake HEI 2010 scores between 60-78.9, exerted > 6 METs of moderate and strenuous activity, spent < 6 hours a day sedentary, consumed less than 4.9 grams of ethanol per day, slept between 7 to 8 hours and were never smokers. In initial age- and race and ethnicity-adjusted analyses, postmenopausal women with an HLI score in T2 (HR: 0.90 [95% CI:0.82-0.98]) and in T3 (HR: 0.81 [95% CI: 0.74–0.89]) (p-trend <0.001) were at reduced risk of breast cancer compared to women in T1. Ongoing analyses include race and ethnicity stratified and fully adjusted multivariable Cox proportional hazards regression. Citation Format: Bethany T. Ogbenna, Iona Cheng, James Butler III, Typhanye Dyer, Xin He, Loic Le Marchand, Lynne Wilkens, Cher Dallal. Association between a healthy lifestyle index and breast cancer risk among post-menopausal women in the Multiethnic Cohort (MEC) Study [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C097.