Cytokeratin 8 (CK8) is an intermediate filament protein produced early in embryogenesis. It is the only type-II CK occurring in many simple epithelial in respiratory, gastrointestinal, male and female reproductive tract and thyroid. CK8 is often co-expressed with Cytokeratin 18. CK8 & CK18 is the major keratin pair in simple-type epithelia, as found in the liver, pancreas, and intestine. CK8 is used to detect adenocarcinomas with simple epithelium origin. The difference in staining pattern is useful to distinguish ductal (peripheral staining) from lobular (perinuclear staining) breast carcinoma.