Spatial Analysis Dissects the Microenvironmental Architecture of Local Recurrence after Breast-Conserving Surgery.

Ipsilateral breast tumor recurrence (IBTR) is a critical prognostic determinant in breast cancer patients undergoing breast-conserving surgery (BCS). The spatial arrangement of immune, stromal, and malignant cells can influence local recurrence progression and treatment efficacy in IBTR tumors. Here, we performed single-cell spatial transcriptomics on primary breast cancer (PBC) and matched IBTR specimens from 22 patients, comprising 18 true recurrence (TR) and 4 new primary (NP) cases, to generate a comprehensive atlas of over 600,000 cells. Cellular neighborhood (CN) analysis identified a specific tumor cell-stromal region significantly enriched in IBTR tumors. Tumor recurrence was driven by a highly proliferative epithelial cell subpopulation characterized by immune exclusion and invasive features. Spatial analysis uncovered a tumor-stromal region where CD24+ tumor cells spatially intersected with BGN+ cancer-associated fibroblasts (CAFs) alongside upregulation of MDK signaling. In parallel, the BGN+ CAFs displayed enriched CXCL12 pathways, suggesting a potential spatial axis that aligns with local immunosuppressive remodeling and recurrent niche formation. Critically, the spatial colocalization of CD24⁺ tumor cells and BGN⁺ CAFs was validated as an independent predictor of recurrence after BCS. This study delivers a high-resolution spatial landscape of IBTR, uncovering distinct microenvironmental landscapes between TR and NP subtypes, and establishes these spatially defined cellular networks as both mechanistic drivers and translatable prognostic biomarkers.