Abstract PS2-07-10: A Single Cell Peripheral Blood Immune Cell Atlas of Breast Cancer Disease States by Race reveals Differences in Peripheral Blood Immune Cell Composition and Functional Pathways

Abstract Background: Racial disparities in breast cancer (BC) are well documented— Non-Hispanic Black (NHB) women are more likely to develop BC at a younger age and experience worse survival outcomes than Non-Hispanic White (NHW) women. Previous studies using pan-cancer cohorts have suggested that changes in peripheral immune cells accompany tumor development. However, in breast cancer, whether the trajectory of these immune changes differs by race across key stages of disease progression, remains poorly understood. To address this gap, we systematically characterized and compared the circulating immune landscape of NHB and NHW women across the continuum of breast cancer progression, from high-risk lesions (HRL) to ductal carcinoma in situ (DCIS) to invasive breast cancer (BC). Methods: PBMCs were isolated from age-matched NHB (HRL:10, DCIS:6, BC:13) and NHW women (HRL:10, DCIS:4, BC:13). scRNA-seq was performed using the 10x Genomics 5’ v2 platform, with data processing by CellRanger (v7.1.0) and Seurat (v5.1.0). Cell types were identified via reference-guided annotation with Azimuth (v0.5.0) and canonical markers. Differentially expressed genes (DEGs) between NWB and NHW were detected using edgeR (v4.4.2, by FDR