Background: Observed racial and ethnic disparities in breast cancer are complex, in part, due to biological and behavioral factors at the individual and neighborhood level. Cardiometabolic factors such as the use of cholesterol-lowering drugs and engaging in healthy lifestyle behaviors may reduce breast cancer risk, however, the current understanding of these factors among diverse racial and ethnic populations remains limited. Moreover, at the neighborhood-level, the extent to which neighborhood socioeconomic status (nSES) influences inflammatory profiles among racially and ethnically diverse populations remains unclear. Using data from the Multiethnic Cohort Study (MEC), this dissertation investigates cholesterol-lowering drug use (Aim I) and a Healthy Lifestyle Index (HLI) (Aim II) in relation to postmenopausal breast cancer risk by race and ethnicity; and, assesses associations between nSES and inflammatory biomarkers among adults (Aim III). Methods: Prospective cohort analyses were conducted among postmenopausal women who completed the third MEC follow-up questionnaire in 2003 (Aim 1, n=41,394) or the baseline questionnaire in 1993-1996 (Aim 2, n=65,561) and were followed until 2017 for invasive breast cancer diagnoses (n=1,681 and 4,555 cases, respectively). Multivariable adjusted hazard ratios [HR] and 95% confidence intervals [95% CI] were estimated using Cox proportional hazards regression. For Aim III, multivariable linear regression assessed cross-sectional associations between nSES and inflammatory serum biomarkers (adiponectin, leptin and C-reactive protein) among adults residing in California (n=6,919) and Hawaii (n=6,899) (2000-2017). Results: Cholesterol-lowering drug use (Aim 1) and duration was not associated with breast cancer risk among all women with no statistically significant heterogeneity in associations by race and ethnicity (p-interaction >0.05). In Aim 2 analyses, women with a higher HLI score (Tertile (T)) had a reduced risk of breast cancer (HRT3 vs T1: 0.76; 95% CI: 0.69, 0.84; HRT2 vs T1: 0.88; 95% CI: 0.79, 0.97) compared to women in the lowest HLI tertile with a significant dose-response observed (p-trend <0.01). Similar patterns were observed across all racial and ethnic groups of women. In California and Hawaii, individuals living in low nSES neighborhoods had higher serum levels of CRP (p-trend <0.001; p-trend = 0.02, respectively) and leptin (p-trend <0.001) while adiponectin levels were lower (p-trend <0.01; p-trend = 0.03, respectively) compared to individuals living in neighborhoods with high nSES. Additional adjustment for body mass index attenuated these associations (p-trend >0.05) (Aim III). Public Health Impact: Findings from this dissertation further support engaging in healthy lifestyle behaviors as a preventative strategy for breast cancer reduction among multiethnic populations of postmenopausal women whereas cholesterol-lowering drug use was not associated with reductions in risk. In addition, residing in low nSES neighborhoods was associated with less favorable inflammatory biomarkers levels.