CK19

CK19 is the lowest molecular weight cytokeratin. This type I keratin is different from other proteins and does not form a pair with type II keratin. It exists in an unpaired form. CK19 (Cytokeratin 19) is found in normal epithelia and tumors of various epithelia origin, especially in monolayer epithelium and mesothelium. It is constant positive in papillary thyroid cancer and less expressed in other types of thyroid cancer, and can be used for differential diagnosis of thyroid tumors. CK19 is not expressed in hepatocytes, which can be used for differential diagnosis of liver cancer and metastatic adenocarcinoma. The strong positive staining of bile duct epithelium in liver tissue of cirrhosis can help distinguish cirrhosis from neoplastic liver tissue. CK19 is usually used for the diagnosis of adenocarcinoma.