This MAb reacts with the rod domain of human cytokeratin-19 (CK19), a polypeptide of 40kDa. Its epitope maps between amino acid 312-335. CK19 is expressed in 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 adenocarcinomas of the colon, stomach, pancreas, biliary tract, liver, and breast. 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 detection of tumor cells in lymph nodes, peripheral blood, bone marrow and breast cancer.