Single-cell RNA sequencing of adenoid cystic carcinoma of the breast reveals cellular heterogeneity and tumor microenvironment features.

BACKGROUND: Adenoid cystic carcinoma of the breast (ACCB) is a rare malignant tumor with distinct pathological features and a relatively favorable prognosis compared to other breast cancer subtypes, yet its molecular mechanisms remain poorly understood due to challenges in sample acquisition and targeted research. METHODS: In this study, we employed single-cell RNA sequencing (scRNA-seq) to systematically characterize the cellular heterogeneity and tumor microenvironment in ACCB. We obtained scRNAseq data from a single patient with ACCB and integrated it with publicly available datasets from head and neck adenoid cystic carcinoma (HNACC) and triple-negative breast cancer (TNBC). Through high-resolution gene expression profiling, cell clustering, differential expression analysis, and cell-cell communication analysis, we aimed to identify key malignant subpopulations and regulatory networks in ACCB. RESULTS: Unsupervised clustering revealed seven major cell types in the analyzed ACCB sample, including epithelial cells, fibroblasts, and immune cells. In-depth analysis of epithelial cells identified H19 + myoepithelial cells (H19 + myoEpC) as the dominant malignant subpopulation, enriched in ACCB compared to other cancers and characterized by high expression of oncogenic pathways and ligands such as LAMB1 and WNT6. Tumor-associated fibroblasts exhibited significant heterogeneity, with cancer-associated fibroblasts (CAFs) expressing EMT-related genes and interacting closely with H19 + myoEpC. The tumor microenvironment was immunosuppressive, with reduced infiltration of CD4 + and CD8 + T cells and B cells, and lacked classical Treg/Tex populations. Comprehensive cell-cell communication analysis showed that H19 + myoEpC orchestrated a signaling network with CAFs, immune cells, and endothelial cells, driving tumor progression and immune evasion. CONCLUSIONS: Our study provides the single-cell resolution map of ACCB from a representative case, highlighting the unique role of H19 + myoEpC in tumor progression and immune suppression. These findings offer new insights into the molecular classification of ACCB and potential therapeutic targets.