Carcinoembryonic antigen (CEA), also known as CD66e, describes a set of glycophosphatidyl inositol and transmembrane cell-surface-anchored glycoproteins involved in cell adhesion, differentiation, anoikis, polarization, and tissue architecture. CEA is present in fetal colon and many types of epithelial tumors, including adenocarcinomas of the GI tract, lung and breast.  CEA staining, along with Calretinin, CK 5/6, D2-40, HBME-1, Napsin A, MOC-31, and Ber-EP4, is used to help differentiate between adenocarcinoma and mesothelioma. Staining with Anti-CEA is also suggested to be useful in identifying the origin of metastatic adenocarcinoma. CEA is an effective marker for adenocarcinomas of the lung, colon, stomach, esophagus, pancreas, gallbadder, urachus, salivary gland, ovary, and endocervix. Antibody to CEA is useful in differentiating lung adenocarcinoma (positive) from mesothelioma (negative). CEA has been helpful in monitoring tumor progression.