CEA (carcinoembryonic antigen), CD66e, comes as either a polyclonal (pCEA) or monoclonal (mCEA) stain.  CEA is generally used as an epithelial marker with strong expression in adencarcinomas.  CEA is strongly expressed in colorectal adenocarcinomas, but it is not a specific marker as many other epithelial tumors may show expression.  CEA is most commonly used as part of a panel to discriminate between metastatic carcinoma (positive) and mesothelioma (negative).

Wick, MR. “Immunohistochemical approaches to the diagnosis of undifferentiated malignant tumor.”Annals of Diagnostic Pathology12(2008):72-84.