Cytokeratin 17 (CK17) is a type I intermediate filament protein encoded by the *KRT17* gene, part of the cytokeratin family crucial for maintaining epithelial cell structure and integrity. It pairs with type II cytokeratins (e.g., CK5) to form a cytoskeletal network, providing mechanical stability and resilience to epithelial tissues. CK17 is primarily expressed in basal and stratified epithelial cells, notably in skin appendages (hair follicles, sweat glands), mammary ducts, cervical epithelium, and certain glandular tissues. Its expression is dynamically regulated during development, wound healing, and pathological conditions.
Notably, CK17 is absent in normal stratified squamous epithelia but is upregulated in hyperproliferative or neoplastic contexts. It serves as a biomarker in diagnostic pathology, particularly for distinguishing epithelial tumors. Overexpression is observed in aggressive carcinomas (e.g., triple-negative breast cancer, pancreatic ductal adenocarcinoma, cervical squamous cell carcinoma) and correlates with poor prognosis. CK17 antibodies are widely used in immunohistochemistry to identify tumor subtypes, such as basal-like breast cancers or squamous cell carcinomas, aiding differential diagnosis. Additionally, CK17's role in cancer progression—linked to epithelial-mesenchymal transition (EMT), invasion, and therapy resistance—makes it a research focus for targeted therapies. Its expression in precancerous lesions (e.g., cervical intraepithelial neoplasia) further highlights its potential in early cancer detection.