585 Background: Breast cancer is the most common malignancy affecting women of all racial and ethnic backgrounds in the United States (US). Although Socioeconomic status (SES), race/ethnicity, and surgical type/delays are associated with breast cancer mortality outcomes, studies on these associations have been contrasting. This study examined the racial/ethnic and SES differences in surgical treatment types and delays. Also, we quantified the extent to which these differences explained the racial/ethnic disparities in breast cancer mortality. Methods: We studied 290,066 women 40+ years old diagnosed with breast cancer between 2010 and 2017 identified from the Surveillance, Epidemiology, and End Results database. We performed logistic regression models to examine the association of SES and race/ethnicity with surgical treatment type and delays. We performed mediation analysis models to quantify the extent to which mortality differences were mediated by treatment, sociodemographic, and clinicopathologic factors. The study subjects were de-identified, and there was no patient contact; thus, the study was exempted from an Institutional Review Board's (IRB) approval. A p-value less than 0.05 indicated significant associations for the descriptive statistics, logistic and Cox proportional hazard regressions, and mediation analysis. We used Stata 17 to perform the analyses. Results: Non-Hispanic (NH) Black [Odds ratio (OR) = 1.16, 95% CI: 1.13-1.19] and Hispanic women [OR = 1.27, 95% CI: 1.24-1.31] were significantly more likely to undergo mastectomy compared to NH White women. Similarly, NH Black and Hispanic women had higher odds of delayed surgical treatment than NH Whites. Patients in the highest SES quintile, compared to those in lowest the lowest, were less likely to experience breast cancer-specific mortality (BCSM). Variations in treatment, SES, and clinicopathological factors significantly explained 70% of the excess BCSM among NH Blacks compared to their NH White counterparts. Conclusions: In conclusion, health disparity continues to be a major societal concern in the US. It affects people of all ages, socioeconomic classes, and ethnic/racial backgrounds. The findings of this study showed that racial and ethnic minorities, the majority of whom have a lower socioeconomic position, are significantly disadvantaged regarding the evaluation, quality, cost, and duration of medical care. Future studies can assess the multifactorial effects of sociodemographic factors like SES, access to health care assessment, and educational background amidst other variables as a multidimensional predictor of treatment delay and overall survival of breast cancer and other health issues among minoritized populations.