Keratin, type II cytoskeletal 8 (UniProt: P11679; also known as Cytokeratin endo A, Cytokeratin-8, CK-8, Keratin-8, K8, Type-II keratin Kb8) is encoded by the Krt8 (also known as Krt2-8) gene (Gene ID: 16691) in murine species. Cytokeratins belong to a diverse group of intermediate filaments that participate in differentiation and maintain the structural integrity of epithelial cells. Cytokeratins share a common structural organization: a central a-helical rod domain flanked by head and tail domains. An important unique feature of cytokeratins is their epithelial cell-type-specific expression. CK8 is a heterotetramer of two type I and two type II keratins. It is expressed in abundance in the epithelia of colon, bladder, ileum, and stomach. CK8 together with KRT19, helps to link the contractile apparatus to dystrophin at the costameres of striated muscle. CK8 is often used together with keratin 18 and keratin 19 to differentiate cells of epithelial origin from hematopoietic cells in tests that enumerate circulating tumor cells in blood. CK8 expression has been correlated with malignancy in leukoplakia and carcinomas of the head and neck and its expression has been observed in all non-small-cell lung cancers.