Cytokeratins are a subfamily of intermediate filament proteins and are characterized by a remarkable biochemical diversity, represented in Human epithelial tissues by at least 20 different polypeptides. They range in molecular weight between 40 kDa and 68 kDa and isoelectric pH between 4.9 – 7.8. The individual Human Cytokeratins are numbered 1 to 20. The various epithelia in the Human body usually express Cytokeratins which are not only characteristic of the type of epithelium, but also related to the degree of maturation or differentiation within an epithelium. Cytokeratin subtype expression patterns are used in the distinction of different types of epithelial malignancies. The Cytokeratin antibodies are of assistance in the differential diagnosis of tumors using immunohistochemistry on tissue sections.

Cytokeratin 14 (CK14) is a 50-kDa keratin expressed in abundance in stratified epithelial cells, epidermal cells, basal cells, mesothelial cells, and myoepithelial cells in various tissues including breast and prostate. CK14 is helpful in the identification of breast cancer with basal phenotype. It has been reported that cytokeratin 5/14-positive breast cancers are true basal phenotype confined to BRCA1 tumors. Along with p63 and CK5, CK14 has been a useful marker for cells with basal, squamous and myoepithelial differentiation.