Whole transcriptome analysis reveals MammaPrint and BluePrint-associated gene expression patterns with early lymph node metastasis in early-stage breast cancer

INTRODUCTION: Early lymph node (LN) metastasis often precedes systemic metastasis and corresponds with significantly inferior survival for patients diagnosed with early-stage breast cancer (EBC). To understand the biological pathways involved in early LN metastasis, differential gene expression (DGE) analysis compared large tumors without evidence of LN metastasis (pT2-3pN0) to small tumors with LN metastasis (pT1pN+). METHODS: This study included 2,349 patients with EBC who underwent MammaPrint and BluePrint testing as part of the FLEX (NCT03053193). DGE was performed between pT2-3pN0/pT1pN + and across their MP/BP subtypes. Immune deconvolution was assessed using gene-signature-based methods, complemented by conventional tumor-infiltrating lymphocyte (TIL) analyses on a representative subset of patients. RESULTS: Greater DGE was observed within the MammaPrint High Risk and BluePrint Luminal B subgroups compared to pathological stages. MammaPrint High Risk tumors saw 73 differentially expressed genes (DEGs), while 34 were found for Luminal B tumors. Gene set enrichment analysis (GSEA) of MammaPrint High Risk/Luminal B tumors showed upregulated proliferation pathways and downregulated epithelial-to-mesenchymal transition (EMT) and immune profiles in pT2-3pN0 vs. pT1pN+, respectively. Immune deconvolution analyses showed a higher abundance of T gamma delta cells and CD4 + Th1 cells and a lower abundance of T regulatory cells, M2 macrophages, and cancer-associated fibroblasts within pT2-3pN0 tumors. Conventional histological assessment revealed no significant differences in TILs. CONCLUSION: This study lays the groundwork for exploring mechanisms of LN metastasis in EBC and their relation to MammaPrint High Risk and Luminal B subtypes. These data support previous studies' association of LN metastasis with EMT and immune dysregulation.