Hypothetical model of the role of EpCAM in breast cancer. EpCAM function might switches from bad to good depending on the phenotype of cancer cells, i.e. their status of epithelial to mesenchymal transition. More epithelium–like cancer cells with strong cytokeratin and E-cadherin expression (T47D, MCF-7) need EpCAM to support proliferation, invasion and tumor angiogenesis. EpCAM knockdown results in fewer invasive and angiogenic tumors in the chicken chorioallantoic membrane (CAM) xenograft model. GFP-positive tumor cells (T) can be monitored on the CAM in real-time and obtain support via the blood vessels (red lines). In contrast, more mesenchyme-like tumor cells, having high vimentin expression, grow independently of EpCAM. Overexpression of EpCAM in these cells disturbs invasion and tumor angiogenesis and prompts strong innate immune responses by the chicken host (blue cells indicate heterophils).