Cytokeratins (CKs), which are biochemically related to intermediate filaments (IFs), form an intracellular network of filaments that is believed to participate in maintaining the structural integrity of cells. Twenty individual polypeptides, divided into two groups, constitute the cytokeratin family.
Each type of epithelial cell can be characterized by its content of cytokeratin polypeptides since the expression pattern varies with the type of epithelium. During transformation of normal epithelial cells into malignant cells, the cytokeratin patterns are usually maintained. This property has enabled the use of cytokerations as histological tumor markers, especially for tumors that are not easily classified.
Cytokeratins 8, 18 and 19 are the most abundant cytokeratins in carcinomas. They are released into necrotic areas and can be found intratumorally and in blood, circulating as partially degraded complexes, and can as such be used as tumor markers. Cytokeratin deposits in tumors make these structures potential targets for radioimmunodetection and immunotherapy. The usefulness of tissue polypeptide antigen (TPA) as a serological tumor marker has been known for a long time. TPA is a molecular complex containing CK8, 18 and 19 and determinations of TPA in serum samples can be used in the follow-up of patients with many types of cancer.
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