Background: Inequities in the receipt of guideline-concordant treatment contribute to worse survival in Black breast cancer (BCa) patients. Inequity reduction interventions (e.g., navigation, bias training, and real-time treatment tracking) may close such treatment gaps. However, evidence to date has been derived from small-scale interventional studies, and the potential impact of these interventions on population-level disparities is unclear. The aim of this study was to simulate the effect of implementing inequity reduction interventions on observed racial inequities in treatment and downstream outcomes after BC diagnosis. Methods: We used data from the North Carolina (NC) Cancer Information and Population Health Resource - which links multi-payer claims to state cancer registry data, for women diagnosed with BCa in 2004-2017 - to calculate Black/non-Black inequities in the receipt of chemotherapy (CTx) within 4 months for women ages <70 with hormone receptor-negative stage Ib-III BCa (n=2,223) and endocrine therapy (ET) within 12 months for stage I-III hormone receptor-positive BCa (n=16,220) in NC. Using effect estimates from trials of inequity-reducing interventions, we simulated the potential increase in the proportion of patients receiving CTx or ET if such interventions were implemented statewide. We estimated the effect of this potential increase in CTx and ET receipt on 10-year BCa mortality by building cohort-, race-, and treatment receipt-stratified simulation Markov models. We report confidence bounds representing 95% of simulation results. Results: Only 70.7% and 72.9% of Black patients in our cohorts received guideline-recommend ET and CTx, respectively, in 2004-2017 (versus 74.3 and 79.4% of non-Black patients, respectively; p<.005). Statewide implementation of inequity reduction interventions could increase ET and CTx receipt among Black patients to 84.3% (79.1-89.3%) and 86.8% (81.5-91.9%), respectively. This would be expected to reduce 10-year BCa mortality among Black patients from 14.2% to 13.6% (13.3-13.9%) in the ET cohort and from 29.4% to 28.7% (28.3-29.1%) in the CTx group. As a result, the racial mortality gap would decrease from 5.7 to 5.2 (4.9-5.5) from 7.0 to 6.6 (6.2-6.9) in the CTx cohorts, respectively. Conclusions: Implementation of interventions designed to reduce treatment inequities are likely to improve cancer care equity. However, increases intreatment receipt alone will not close the BCa mortality gap. Inequities at other points on the cancer continuum, such as in pre-diagnostic risk factors, screening, diagnostic work-up, and post-treatment factors, may explain residual gaps which will require more comprehensive interventions to achieve full equity in breast cancer outcomes.