Cytokeratin18 (CK18)

CK18 is a low molecular weight keratin with a molecular weight of 45KDa. CK18 is ubiquitously expressed in monolayer and pseudostratified epithelium, whereas it is usually negative in stratified squamous epithelium. It is often used to determine whether a tumor, including metastatic cancer, is of simple epithelial origin. It is mainly used to distinguish Merkel cell carcinoma from basal cell carcinoma, and distinguish seminoma from malignant melanoma.