Description
Cytokeratin 17 (CK17, Keratin 17) is a member of the Cytokeratin subfamily of intermediate filament proteins (IFPs). It is unique in that it is normally expressed in the basal cells of complex epithelia but not in stratified or simple epithelia. Cytokeratin 17 is expressed in the nail bed, hair follicle, sebaceous glands and other epidermal appendages. Antibody to cytokeratin 17 is an excellent tool to distinguish myoepithelial cells from luminal epithelium of various glands such as mammary, sweat and salivary. It is expressed in epithelial cells of various origins, such as bronchial epithelial cells and skin appendages. It may be considered as 'epithelial stem cell' marker because cytokeratin 17 antibody marks basal cell differentiation. Cytokeratin 17 can be useful when included in a panel of antibodies against TTF-1, napsin A, CK5&6, p63, and SOX-2 for diagnostic differentiation between lung adenocarcinoma (LADC) and lung squamous cell carcinoma (SCLC), especially for poorly-differentiated lung carcinoma. Cytokeratin 17 is expressed in SCLC much higher than in LADC. In breast carcinomas, approximately 20% of patients show no expression of ER, PR and Her2, which are defined as triple negative tumor. Eighty-five percent of the triple negative breast carcinomas immunoreact with basal cytokeratins including cytokeratin 17 antibody. Also important is that cases of triple negative breast carcinoma with expression of keratin 17 show an aggressive clinical course. The histologic differentiation of ampullary cancer, intestinal vs. pancreatobiliary, is very important for treatment. Usually antibody to cytokeratin 17 and MUC1 immunoreactivity represents pancreatobiliary subtype whereas antibody to MUC2 and CDX2 positivity defines intestinal subtype