The molecular profile of breast cancer: primary tumor versus corresponding lymph node metastases

Breast cancer (BrCa) is the most frequent malignancy in female, and lymph node metastases (LNM) is an important prognostic and therapeutic parameter. The molecular classification is nowadays largely applied to characterize the primary tumors, but few studies focused on the comparison between the molecular profiles of the primary with corresponding LNM. In the current work, we investigated the expression of conventional markers used by molecular classification in both primary tumors and axillary LNM. A series of 156 patients with BrCa was investigated, and from these 80 cases showed LNM. After routine pathological investigation, including the histopathological form and grade, we performed additional step sections from the primary and lymph nodes for immunohistochemistry. All procedures for hormone receptors, human epidermal growth factor receptor 2 (HER2), Ki67, cytokeratin 5 (CK5), epidermal growth factor receptor (EGFR), p53, E-cadherin, and B-cell leukemia∕lymphoma-2 (Bcl-2) were performed using the standard automated procedures. We found significant differences between the primary tumors and corresponding LNM in luminal A, luminal B, and basal-like carcinoma. No phenotypical interconversions were noticed in HER2 and unclassified BrCa. Our data demonstrate that in almost 20% of the cases the molecular profile of the primary does not overlap with aspects found in the lymph nodes. Our results strongly suggest performing the molecular classification in both primary tumors and in LNM. Current data suggest that the application of this diagnostic procedure will significantly influence the therapeutic strategy.