CD133 immunoreaction appeared to be expressed at the apical/endoluminal surface of tumor cells forming a lumen, as reported in a small series of primary ovarian carcinomas [27], as well as in pancreatic [22,24], and gastric carcinoma [34], while it was mainly localized in the cytoplasm of cells forming solidly arranged tumors. Here, PROM1 is linked to gastric carcinoma.