Keratins are cytoplasmic intermediate filament proteins expressed by epithelial cells. Cytokeratin, AE1/AE3, is a keratin cocktail that detects CK1-8, 10, 14-16 and 19; it is non-reactive with CK17 or CK18. It recognizes epithelial cells of normal and abnormal human tissues. Therefore, it has been used to characterize the source of various neoplasms and to study the distribution of keratin containing cells in epithelia during normal and neoplastic development. This antibody is useful to distinguish epithelial carcinoma from non-epithelial malignancies.

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