Keratins are cytoplasmic intermediate filament proteins expressed by epithelial cells. Keratin 7 (K7) is expressed in a wide range of epithelial structures in humans. K7 occurs in the columnar and glandular epithelium of the lung, cervix, breast, in bile ducts, collecting ducts in the kidney and in mesothelium, but is absent in gastrointestinal epithelium, hepatocytes, proximal and distal tubules of the kidney and myoepithelium.The antibody OVTL 12/30 is an excellent tool in the differential diagnosis of malignant cells and to determine primary tumor localization. It stains a 54 kD protein band of cytoskeletal proteins from cell lines in one and two dimensional immunoblots.