Transcription factors associated with epithelial-mesenchymal transition and cancer stem cells in the tumor centre and margin of invasive breast cancer.

Although tumor surgery aims for a complete resection respecting tumor-specific safety distance, in many cases the most peripheral part, the invasion front, remains in situ. Tumor cells at the tumor margin lose epithelial properties and acquire features of mesenchymal cells. The process of epithelial-to-mesenchymal transition (EMT) has been suggested to be of prime importance for tissue and vessel invasion. Recently, features of EMT were shown to be linked to cells with tumor-founding capability, so- called cancer stem cells (CSC). In this study we show that transcription factors associated with EMT markers Snail, Slug, Twist and Zeb1 are differentially expressed between normal breast epithelium, ductal carcinoma in situ and invasive breast cancer. Both invasive and in situ carcinoma expressed less Slug and Twist and more Zeb1 compared to normal epithelium. Using fluorescence multi-staining the number of potential CSC among invasive cancer cells varied dramatically depending on the staining combination used (18.5% for CD44(+)/CD24(-) and 2.4% for CD49f(+)/CD24(+)). Interestingly, neither transcription factors associated with EMT nor potential CSC counts varied between tumor centre and invasion front. No association of these features with clinical outcome was detected. Our results suggest that reliable in situ markers for EMT are missing for invasive breast cancer. Alternatively, the process of EMT might be activated in tumor cells at the margin as well as the centre. Furthermore, our data show that the bio-markers of CSC detect very variable cell populations within breast cancer, challenging the assumption of a hierarchical organization of CSC in these tumors.