Multi-omics analysis identifies the unique high-FDCSP basal cells in triple-negative breast cancer

Follicular dendritic cell secreted protein (FDCSP) is highly expressed in various cancers and has been implicated in tumor migration and invasion, yet its role in triple-negative breast cancer (TNBC) remains poorly understood. Our findings revealed that FDCSP expression was significantly elevated in TNBC compared to normal breast tissue, whereas its expression was significantly reduced in non-TNBC. In TNBC, high FDCSP expression was associated with an increased mutation rate of TP53 and influenced the infiltration of B cells and macrophages. Single-cell transcriptome analysis demonstrated that FDCSP was predominantly highly expressed in basal cells but exhibited low expression in luminal epithelial cells. This observation was further corroborated by spatial transcriptome (ST) analysis. Immunohistochemistry (IHC) assay also confirmed the distinct expression patterns of FDCSP. Cell-cell interaction and receptor-ligand pair analyses indicated that macrophages could interact with the receptor epidermal growth factor receptor (EGFR) in FDCSP highly expressed basal cells by secreting transforming growth factor-β1 (TGF-β1). Then, the co-localization of FDCSP and EGFR in TNBC basal cells was verified by IHC and immunofluorescence (IF) assay. Additionally, we discovered that FDCSP possesses strong predictive capabilities for distinguishing between responders and non-responders to Immune checkpoint blockade (ICB) treatment. Finally, leveraging the CARE database, we identified 14 potential FDCSP-related target drugs. These findings highlight the unique expression pattern of FDCSP in breast cancer, revealing FDCSP as a promising target for therapeutic strategies in TNBC.