11568 Background: Many Adolescent and Young Adult (AYA) Breast Cancer (BC) patients receive chemotherapy as part of their initial treatment. Long-term bone marrow suppression is a potential complication, but no studies have evaluated the impact of race/ethnicity on the development in AYA BC survivors. Methods: Female patients ages 15-39 diagnosed with BC during 1996-2012 and surviving ≥ 2 years were obtained from the California Cancer Registry and linked to statewide hospitalization data. We estimated the cumulative incidence of developing anemia, leukopenia, or major infection/sepsis (≥ 2 years after diagnosis), accounting for death as a competing risk, and examined the impact of race/ethnicity using multivariable Cox proportional hazards regression. Results: Of 14,729 patients, 48.8% were non-Hispanic white, 8.3% non-Hispanic black, 25.5% Hispanic, and 16.5% Asian/Pacific Islander. At diagnosis, 95.5% had local or regional disease (27.7% stage I, 49.4% stage II), and were mostly treated with surgery (96.2%) and chemotherapy (74.3%). The 10-year cumulative incidence of anemia (16.8% vs 11.7%), leukopenia (4.6% vs 2.1%), and major infection/sepsis (13.2% vs 7.9%) was greater following initial treatment with chemotherapy (p < 0.0001 for all vs no chemotherapy). In multivariable analyses controlling for sociodemographic factors, baseline comorbidities, treatment and stage, Blacks had the highest risk (vs. non-Hispanic whites) of medical late effects, including anemia [HR: 1.62, CI 1.41-1.86], leukopenia (HR: 1.53, CI 1.17-2.00), and major infection/sepsis (HR: 1.36, CI 1.16-1.60). Similarly, Hispanic and Asian/Pacific Islanders had a higher risk of developing anemia (HR: 1.16, CI 1.04-1.29; HR: 1.17, CI 1.03-1.33) and trended toward developing more leukopenia (HR: 1.24, CI 1.00-1.54; HR: 1.25, CI 0.98-1.61). Conclusions: AYAs of Black, Hispanic, and Asian/Pacific Islander race/ethnicity are at an increased risk of anemia and leukopenia after chemotherapy compared with non-Hispanic Whites. With improvements in prognostic testing resulting in potential decreased chemotherapy usage, there may be a decrease in long-term late effects for these young cancer survivors.