EpCAM overexpression in vivo leads to hyperplastic cell growth without ductal lumen formation. HMECs were transplanted together with matrigel into the chorioallantoic membrane (CAM) of chicken embryos and cell growth and morphology analyzed after 6 days. (A) Chicken embryos with HMEC xenografts. White arrows indicate transplants of HMECs in matrigel plugs (B) Fluorescence stereo microscope picture of a HMEC graft 6 days after in vivo growth. The green clusters (adenoviral GFP) indicate human cell-cell aggregates that growth inside the CAM (magnification 20×) (C) Immunohistochemical analysis of cross-sections of HMEC grafts in the CAM. Sections were stained with an antibody specific for human cadherin, thus detecting only human cells. In contrast to GFP transfected controls, EpCAM overexpressing grafts show bigger glandular structures that lack formation of lumen. (D) Immunohistochemical analysis of p63high progenitor cells. Noteworthy, HMECs at the glandular base express the progenitor marker p63. EpCAM overexpressing clusters are surrounded by significant bigger clusters of chicken leukocytes (black arrows). Bars indicate 50 μm, asterisks indicate lumen.