BACKGROUND: Racial and ethnic disparities in guideline-recommended breast cancer treatment are well documented, however studies including diagnostic and staging procedures necessary to determine treatment indications are lacking. The purpose of this study was to characterize patterns in delivery of evidence-based services for the diagnosis, clinical workup, and first-line treatment of breast cancer by race-ethnicity. METHODS: SEER-Medicare data were used to identify women diagnosed with invasive breast cancer between 2000 and 2017 at age 66 or older (n = 2,15,605). Evidence-based services included diagnostic procedures (diagnostic mammography and breast biopsy), clinical workup (stage and grade determination, lymph node biopsy, and HR and HER2 status determination), and treatment initiation (surgery, radiation, chemotherapy, hormone therapy, and HER2-targeted therapy). Poisson regression was used to estimate rate ratios (RR) and 95% confidence intervals (CI) for each service. RESULTS: Black and American Indian/Alaska Native (AIAN) women had significantly lower rates of evidence-based care across the continuum from diagnostics through first-line treatment compared to non-Hispanic White (NHW) women. AIAN women had the lowest rates of HER2-targeted therapy and hormone therapy initiation. While Black women also had lower initiation of HER2-targeted therapy than NHW, differences in hormone therapy were not observed. CONCLUSIONS: Our findings suggest patterns along the continuum of care from diagnostic procedures to treatment initiation may differ across race-ethnicity groups. IMPACT: Efforts to improve delivery of guideline-concordant treatment and mitigate racial-ethnic disparities in healthcare and survival should include procedures performed as part of the diagnosis, clinical workup, and staging processes.