Abstract BACKGROUND: Determinants of racial inequities in risk of subtype-specific breast cancers are poorly understood. Features of the neighborhood context may contribute to racial inequities along the breast cancer continuum, however few have examined subtype-specific incidence. Therefore, this study aimed to characterize the association between the neighborhood racial context (housing discrimination and racial composition) and race- and subtype-specific breast cancer incidence among NH Black and NH White women in California. METHODS: We merged data from the California Cancer Registry on women aged 20+ diagnosed with primary breast cancer between 2006-2015 with neighborhood racial context at time of diagnosis: census tract % NH Black and a new racial bias index derived using 2007-2013 data from the Home Mortgage Disclosure Act. We used Poisson regression to estimate associations between neighborhood racial context and race- and Luminal A and TNBC (triple-negative breast cancer)-specific incidence rates, adjusting for neighborhood confounders. RESULTS: We identified n=104,716 cases of Luminal A and n=15,739 cases of TNBC over the study period. Among Black women, living in a high % Black census tract was associated with higher incidence of Luminal A (IRRadj=1.16 (1.08, 1.24)) and TNBC (IRRadj=1.17 (1.04, 1.32)) subtypes, relative to residence in low % Black tracts. No statistically significant association between neighborhood racial composition and either subtype was observed among NH Whites, nor between racial bias in mortgage lending and breast cancer among either racial group. CONCLUSION: Neighborhood racial composition may proxy cross-cutting social and environmental risk factors for breast cancer, regardless of subtype. These exposures may disproportionately burden Black versus White women with respect to breast cancer risk. Citation Format: Eli K. Michaels, Kirsten M.M. Beyer, Yuhong Zhou, Alison J. Canchola, Salma Shariff-Marco, Scarlett L. Gomez. Neighborhood racial context and race- and subtype-specific breast cancer incidence among non-Hispanic Black and non-Hispanic White women in California, 2006-2015 [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 C061.