Atlas of Breast Cancer in Chinese Young Women Revealed by Single-cell RNA and ATAC Sequencing

Young women with breast cancer (YBC, age⩽40) are particularly prevalent in Asian. YBCs usually show more aggressive pathology and poorer outcomes than non-young patients. However, YBCs are underrepresented in current BC risk models, with their tumor intrinsic subtypes and microenvironments lacking a systematic elucidation at the single-cell level, thereby limiting the young-specific therapies. We established a single-cell Chinese YBC landscape baseline, including 246,659 cells, by applying scRNA-seq and scATAC-seq on untreated patients. We developed a cross-modal feature selection algorithm to construct a young-intrinsic subtype classifier ‘BCYtype’, outperforming existing classifiers in pseudobulk, cellular, and external cohorts. Comparative analyses with non-young samples revealed a direct differentiation trajectory from mammary stem cells to mature luminal cells. Pseudotemporal analysis also demonstrated that tumor cells in younger patients undergo earlier carcinogenesis. Mechanistically, we found that CDH1 interacts with pTex and NKT cells, serving as a young-specific marker and a potential therapeutic target for HR+ young patients. The interaction between exhausted T cells and antigen-presenting cells revealed NKG2A as a candidate therapeutic target for triple-negative breast cancer in young patients.