Test Details: Immunohistochemical testing is carried out on biopsy/resected tissue specimen. This testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. Cytokeratin 20 is constantly expressed by adenocarcinoma of the gastrointestinal tract, pancreas, and extrahepatic bile duct system, mucinous ovarian carcinoma, and less frequently transitional cell carcinoma.