e18565 Background: The persistent racial and socioeconomic status (SES) disparities in breast cancer outcomes are partially attributed to propensity towards more aggressive cancers or presentation at higher stages among these groups. Chronic stressors related to race and SES are another major mechanism underlying these inequities. This study aims to examine the effect of race and SES within the AJCC 8th-edition staging system, which incorporates anatomic extent of disease and tumor biology. Methods: The SEER breast cancer database linked with county-level census data was used to identify patients with invasive breast cancer from 2010-2015. The database includes a composite SES-index which was analyzed in quintiles. Cox proportional-hazards regression was used to estimate disease-specific survival (DSS). Results: 259,852 patients were included: 176,369 (67.9%) non-Hispanic white, 28,510 (11.0%) Black, 29,737 (11.4%) Hispanic, and 22,887 (8.8%) Asian. Black race, lower SES, public insurance, lower education, and increased poverty were associated with decreased DSS. Adjusted survival analysis for patient, SES, tumor, and treatment characteristics demonstrated that patients of black race had inferior DSS within each stage. Fully adjusted models also showed patients residing in lower SES counties had inferior DSS [Table]. Conclusions: Racial and SES disparities in breast cancer-specific mortality were evident across all stages of disease. Future efforts to improve breast cancer outcomes should systematically assess and address racial and socioeconomic factors as fundamental drivers of inequitable outcomes. Adjusted 5-year DSS Estimates, Stratified by Race and SES.[Table: see text]