Cytokeratin 19 (CK19) forms intermediate filaments found in the intracytoplasmic cytoskeleton of epithelial tissue and provides mechanical support. Anti-Cytokeratin 19 stains epithelia and epithelial malignancies such as carcinomas of the colon，stomach，pancreas，biliary tract，liver，and breast. Cytokeratin 19 is a useful marker for distinguishing hepatocellular carcinoma from intrahepatic cholangiocarcinoma. This differentiation is improved when stained in combination with Cytokeratin 7，CAM5.2l，Ber-EP4/MOC31，HepPar1 and TTF1. Cytokeratin 19 staining can also be used to recognize thyroid papillary carcinomas.
