Overexpression of EpCAM in MDA-MB-231 xenografts. MDA-MB-231TetR EpCAM cells were grafted into chicken embryos and in vivo growth analyzed after five days in the presence and absence of tetracycline. In vivo experiments were performed with at least 12 embryos per group and 4 onplants/CAM. (A) Cross-sections of tumor xenografts in host tissue were analyzed by immunohistochemistry for EpCAM protein. Tumor invasion front into host tissue is indicated by a red line. (B) Tumor cells were stained for E-cadherin expression to indicate specifically human tumor cells. (C) Proliferating human tumor cells were stained for the expression of Ki67. (D) Mesenchyme-like human tumor cells were stained for the marker vimentin (vim). Note the massive clusters of chicken heterophils in EpCAM-high tumors (blue area) that incorporate between tumor cells in the invasion front (yellow arrows). Magnification: 100 x.