Comparative Analysis of Epithelial-Mesenchymal Transformation Markers in Primary Focus, Tumor "Buds" and Metastatic Lymph Nodes

Background: Breast cancer is a heterogeneous disease with distinct molecular subtypes, each exhibiting unique clinical and pathological characteristics. The HER2-positive subtype, characterized by the overexpression of the HER2 protein, is associated with aggressive tumor behavior and poor prognosis. Epithelial-mesenchymal transition (EMT) is a critical process in tumor invasion, metastasis, and resistance to therapy, particularly in HER2-positive breast cancer. Tumor-infiltrating lymphocytes (TILs) play a crutial role in the host's immune response against cancer and have been correlated with clinical outcomes in various cancers, including breast cancer. Objective: This study aimed to investigate the phenotypic heterogeneity of EMT in different tumor sites, including the primary tumor focus, tumor "Buds," and metastatic lymph nodes in HER2-positive invasive ductal carcinoma (IDC). We focused on assessing the expression of EMT markers (E-cadherin, Beta-catenin, Vimentin) and their correlation with TILs, to understand their potential implications for clinical outcomes and personalized treatment strategies. Methods: A retrospective analysis was conducted on 130 cases of HER2-positive IDC. Archival formalin-fixed, paraffin-embedded (FFPE) tissue blocks from 2018-2024 were selected based on strict inclusion criteria. Immunohistochemistry was performed to evaluate the expression of EMT markers and other relevant proteins, including Androgen Receptor, PD-L1, Ki67, and p53, across four tumor components: two primary tumor foci, tumor Buds, and metastatic lymph nodes. Quantitative data were analyzed using Spearman's rank correlation, Mann-Whitney U, and Kruskal-Wallis tests, with significance set at p < 0.05. Results: The study revealed significant heterogeneity in EMT marker expression across different tumor sites and stages. The mean percentage of TILs was highest at T1 stage (46.25%) and lowest at T4 stage (17.5%), with a strong negative correlation between TILs and tumor stage (r = -0.599). Vimentin expression showed a positive correlation with tumor stage, particularly in tumor Buds and lymph nodes, indicating a mesenchymal phenotype associated with advanced stages. E-cadherin expression decreased with tumor progression, with the lowest expression observed at T4 stage, suggesting a loss of epithelial characteristics. Beta-catenin expression increased across stages, with the highest levels in tumor Buds and lymph nodes at T4 stage. Conclusion: The findings suggest that EMT is a heterogeneous and stage-dependent process in HER2-positive IDC, with distinct expression patterns of EMT markers across different tumor sites. The correlations between EMT markers, TILs, and tumor stage underscore the potential of these markers as prognostic indicators and therapeutic targets. Identifying specific EMT profiles in different tumor microenvironments could enhance the development of personalized treatment strategies for patients with HER2-positive breast cancer, ultimately improving clinical outcomes. Further research is needed to elucidate the underlying mechanisms driving EMT heterogeneity and validate these findings in larger cohorts.