This Ab reacts with the rod domain of human cytokeratin 19 (CK19), a polypeptide of 40kDa. CK19 is expressed in the sweat gland, mammary gland ductal and secretory cells, bile ducts, gastrointestinal tract, bladder urothelium, oral epithelia, esophagus, and ectocervical epithelium. Anti-CK19 reacts with a wide variety of epithelial malignancies, including colon, stomach, pancreas, biliary tract, liver, and breast adenocarcinomas. Perhaps the most useful application is the identification of thyroid carcinoma of the papillary type, although 50%-60% of follicular carcinomas are also labeled. Anti-CK19 is a useful marker for detecting tumor cells in lymph nodes, peripheral blood, bone marrow, and breast cancer.