RNA-seq Profiling of Draining and Metastatic Lymph Nodes in HER2-Positive Breast Cancer Identifies POSTN as a Prognostic Marker

HER2-positive breast cancer is clinically aggressive and frequently disseminates to regional lymph nodes, yet the transcriptomic programs associated with nodal spread remain incompletely defined. Here, we profiled matched tumor-draining lymph nodes (TDLN) and metastatic tumor-involved lymph nodes (TMLN) from six patients with HER2-positive breast cancer using RNA sequencing (RNA-seq). Differential expression analysis was performed with DESeq2, applying Benjamini-Hochberg correction (FDR < 0.05) and an absolute log2 fold-change threshold (|log2FC| ≥ 1). We identified 237 differentially expressed genes (182 upregulated and 55 downregulated in TMLN vs. TDLN). Functional enrichment analyses highlighted extracellular matrix (ECM)-receptor interaction, PI3K-AKT signaling, focal adhesion, and cholesterol metabolism as prominent pathways associated with metastatic lymph nodes, suggesting coordinated ECM remodeling and signaling activation during nodal dissemination. Among the most upregulated genes, POSTN emerged as a key candidate and was further linked to adverse clinicopathologic characteristics. In an independent validation cohort (n = 120), higher POSTN expression was associated with inferior disease-free survival. Collectively, these results nominate POSTN as a potential prognostic biomarker and support ECM-centered and PI3K-AKT-related mechanisms as actionable biological features of lymph-node metastasis in HER2-positive breast cancer.