Keratins are cytoplasmic intermediate filament proteins expressed by epithelial cells. CK10 is a type I keratin seen in all suprabasal cell layers including stratum corneum. Cytokeratins have been found to be useful markers of tissue differentiation which is directly applicable to the characterization of malignant tumors. Cytokeratins 10 and 13 are present in the cytoskeletal region of a subset of squamous cell carcinomas.