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 7 (CK7) is a cytoplasmic intermediate filament protein expressed on most ductal and glandular epithelium including lung, breast, bladder and female genital tract, but not in most gastrointestinal epithelium, prostate, hepatocyte and squamous epithelium. CK7 expression is absent in colon cancer, prostate cancer and squamous carcinomas. The restricted expression of CK7 in some epithelium makes it useful to identify the organ origin of adenocarcinomas when combined with staining of Cytokeratin 20 and other cell specific markers.