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.