CD133 expression in pancreatic ductal adenocarcinomas. A-D) Variable expression in carcinomas of high (A, B) and low (C, D) differentiation grade. The insert in A is a high magnification of a cancerous duct with intense CD133 positivity in amorphous, intraductal material. E, F) Rare, single tumor cells with cytoplasmic staining (arrows). G) CK19-CD133 double staining of a malignant duct. Note cytoplasmic CD133 expression (brown) in a CK19-negative cell group (arrow) and co-expression of both markers in cells surrounding the lumen (asterisk). H-J) Staining (asterisks) at the apical/endoluminal membrane surface and surface of papillary arranged tumor cell clusters in a malignant duct (H), in a vessel of a primary tumor (I) and in a vessel of a lymph node metastasis (J). A-D = ×200, scale bar in A = 100 μm. E-G = ×1000, scale bar in A = 20 μm. H, J = ×400, scale bar in A = 50 μm. I = ×630, scale bar in A = 32 μm.