Fig. 1

Cytokeratin 18 (CK18) expression in normal tissues. The images show strong CK18 staining in epithelial cells from rectum (a) and pancreas (b), a zonal staining variability in the liver (c), strongly positive umbrella cells and a gradually decreasing staining intensity from superficial to basal urothelial cells in the bladder (d), strong positivity in acinus cells but absent staining in basal cells of the breast epithelium (e) and a complete lack of staining in squamous epithelium of the oral mucosa (f)