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Purpose: The bone marrow is a frequent and clinically important homing site for early disseminated breast cancer cells. Here, we aimed to profile the protein expression of these cells using unique cell line models and to evaluate the prognostic relevance of candidate gene expression for breast cancer patients., Experimental Design: To identify expression patterns characteristic for micrometastatic cells, three different cell lines (BC-K1, BC-P1, and BC-S1) established by SV40 immortalization of cancer cells isolated from the bone marrow of patients with breast cancer were compared with MCF-7 breast cancer and SV40 immortalized normal breast ductal cells (MTSV-1.7) using two-dimensional gel electrophoresis followed by MALDI-ToF analysis. The prognostic significance and clinicopathologic associations of selected differentially expressed proteins were evaluated using high-density breast cancer tissue microarrays., Results: In contrast to MCF-7 and MTSV1-7 reference cell lines, all micrometastatic cancer cell lines displayed loss of epithelial cytokeratins (CK8, CK18, and CK19) and ectopic expression of vimentin commonly present in mesenchymal cells. Immunohistochemical analysis of 2,517 samples of breast cancer further showed that loss of cytokeratin and ectopic vimentin expression were significantly associated with a higher tumor grade, high mitotic index, and negative estrogen/progesterone-receptor status. Although in univariate analyses significantly related to clinical outcome, none of the cytokeratins analyzed were independently associated with either overall or cancer-specific survival., Conclusions: Micrometastatic cancer cells exhibit marked changes in the expression pattern of cytoskeletal proteins indicative of an epithelial-mesenchymal transition. This phenotypical change could already be detected in primary tumors and is associated with the aggressive behavior of breast cancer cells in vivo.

Purpose: EMMPRIN (extracellular matrix metalloprotease inducer) is a glycosylated member of the immunoglobulin superfamily known to stimulate the production of matrix metalloproteases (MMPs) 1, 2, and 3 and MT1-MMP in peritumoral fibroblasts. We here evaluated whether EMMPRIN expression is related to tumor progression in human breast cancer., Experimental Design: An immunohistochemical study using high-density tissue microarrays (n = 2222 breast cancer samples) and EMMPRIN-specific antibodies HIM6 and MEM-M6/1 was performed, and staining results were statistically correlated with various clinicopathological parameters. To analyze the putative association between EMMPRIN expression and bone marrow (BM) micrometastasis, an additional set of 55 breast tumors from patients with or without micrometastatic cells as determined with anti-cytokeratin antibody A45-B/B3 were included in our study. Cytokeratin-positive cells in BM were costained with EMMPRIN-specific antibody 1G6.2., Results: Positive EMMPRIN staining correlated significantly with various histopathological risk factors (higher tumor grade, increased tumor size, negative estrogen receptor status and progesterone receptor status, and higher mitotic index) as well as decreased tumor-specific survival (log-rank, P = 0.0027). In particular, in patients > 50 years (i.e., postmenopausal women), EMMPRIN expression was an independent prognosticator as shown by Cox regression analysis (relative risk = 1.7, 95% confidence interval 1.4-4.3, P = 0.036). An involvement of EMMPRIN in tumor progression was also supported by the fact that it was expressed on approximately 90% of micrometastatic cells in BM., Conclusions: EMMPRIN expression in primary tumor predicts an unfavorable prognosis in breast cancer, suggesting a crucial role of EMMPRIN in progression of human mammary carcinomas.