medical Definition of cytokeratin
: any of a class of fibrous proteins that are intermediate filaments of the cytoplasm of epithelial cells, provide structural support to the cytoskeleton and play a role in various cellular functions (as differentiation), are made up of paired polypeptide chains of which one chain is acidic and of low molecular weight and the other is basic or neutral and of high molecular weight, and are sometimes used as markers to identify malignancies of epithelial origin
