Cytokeratin 8(CK8) is an intermediated filament protein with a molecular weight of 52 KD. It is a member of cytokeratin type II family. Cytokeratin 18(CK18) is an intermediated filament protein with a molecular weight of 45 KD, belongs to type I cytokeratin family. They are widely expressed in monolayer epithelial cells of thyroid , breast , gastrointestinal tract and respiratory tract. Cytokeratin 8/18 is often used as a useful marker to identify adenocarcinoma from simple epithelial cells.Cytokeratin 8/18 pair are normally expressed in simple epithelia, but not in stratified epithelial cells. Research indicates that squamous cell carcinomas derived from stratified epithelia show abnormal expression of Cytokeratin 8/18, although it is not known whether these proteins contribute to the malignant phenotype of the cells. Expression of Cytokeratin 8/18 in oral squamous cell carcinomas is an independent prognostic marker that indicates a poor prognosis.