Cytokeratin19 (CK19)

CK19 is a low molecular weight keratin with a molecular weight of 40KDa. CK19 is present in normal epithelium and tumors of various epithelial origins, especially in monolayer epithelium and mesothelium. CK19 is often used to determine the epithelial origin of tumors. It is positive in papillary thyroid carcinoma, but less in other types of thyroid cancer. Follicular adenoma is generally negative so this feature can be used for the diagnosis of follicular papillary carcinoma. Liver cells do not express CK19, which can be used to differentiate hepatocellular carcinoma from cholangiocarcinoma and metastatic carcinomas.