CEA specifies a group of proteins in the Carcinoembryonic Antigen (CEA) family of proteins which are present in the epithelia of various types and tumors (both benign and malignant) derived from such epithelia. Such tissues are represented by the epithelia of colon, bronchus, alveoli, breast, pancreas, biliary tract, superficial layer and parietal layers of the stomach. Predominately biliary canaliculi are labelled in the liver and this factor is useful in the diagnosis of hepatocelluar carcinoma. CEA has been quite useful in differentiating adenocarcinoma of the lung vs. mesothelioma.