Neighborhood Racial and Ethnic Composition Typology and Breast Cancer Risk: The Multiethnic Cohort Study.

Living in racially and ethnically segregated neighborhoods may increase the risk of breast cancer. We examined associations between neighborhood racial and ethnic composition typology and incident primary invasive breast cancer risk in a population-based sample of 102,615 African American/Black, Japanese American, Native Hawaiian, Latino, and White females residing in California and Hawaii from the Multiethnic Cohort (MEC) study between 1993-2019. Hazard ratios (HRs) and 95% confidence intervals (CI) were estimated using multivariable Cox proportional hazards regression. In California, African American/Black females in predominantly White neighborhoods had decreased breast cancer risk compared to African American/Black females in predominantly Black neighborhoods (HR=0.71, 95% CI=0.50-0.99). Latino females in mixed White and Asian American/Pacific Islander neighborhoods had increased breast cancer risk (HR=1.59, 95% CI=1.20-2.11) in comparison to Latino females in predominantly Hispanic neighborhoods. In Hawaii, Japanese American females in multiethnic neighborhoods had increased breast cancer risk (HR=1.49, 95% CI=1.24-1.78) compared to Japanese American females in predominantly Asian American neighborhoods. Native Hawaiian females in predominantly Asian American neighborhoods had increased breast cancer risk (HR=1.23, 95% CI=1.04-1.45) compared to Native Hawaiian females in mixed Native Hawaiian neighborhoods. Our findings can inform future studies to identify specific pathways through which segregation influences cancer risk in multiethnic populations.