any human breast cancer cell lines have been in culture for several years, serving as model systems for studying aspects of breast cancer biology. Molecular alterations might occur in these cells during cultivation, and it remains unknown to which extent findings in these cell lines can be related to human disease. Hereby, we describe the establishment of a breast cancer cell line, MW1, from malignant pleural effusion. We compare expression patterns of several molecular markers in breast biopsy tissue, in cultivated tumor cells derived from pleural effusion reflecting the metastatic state, and in late passages of a lineage derived from the pleural culture. Our data show that expression of estrogen and progesterone receptors was lost in the cultivated tumor cells derived from pleural effusion as shown by immunohistochemical staining. Cytokeratin expression patterns remained luminal. During cultivation, the growth rate of MW1 cells increased dramatically and the morphology underwent alterations. As shown by Western blotting, E-cadherin expression remained unchanged whereas P-cadherin expression had increased after 4 years of cultivation of the cell line. Integrin β4 expression was low in early passages of the pleural effusion whereas the cell line exhibited high expression levels of β4. HGF receptor (c-Met), EGF receptor, VEGF and VEGF receptor-2 (KDR) expression was detectable by semiquantitative RT-PCR and remained unchanged during cultivation. In contrast, VEGF receptor-1 (flt-1) expression showed lower expression after 4 years of cultivation. The cell line migrated towards HGF, but not towards VEGF. This study provides exemplary insight into the molecular metamorphosis tumor cells undergo in vivo or in vitro on their way from the primary tumor via an equivalent of the metastatic state and during the development of a clonal cell line.

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