Cytokeratin 7 is a 54kD intermediate filament protein found in a variety of glandularepithelia. Cytokeratin 7 has been found in columnar and glandular epithelium of the lung, cervix, breast, bile ducts and larger collecting ducts of the kidney. It is present in the transitional epithelium of bladder as well as ovarian and lungepithelia, and occasionally staining of blood vessel cell walls, particularly endothelial cells, may be observed. However, Cytokeratin 7 is not expressed by epithelial cells of the gastrointestinal tract, colon or prostate. Keratin 7 is often co expressed with keratin 19.