KRT13 (Cytokeratin 13, CK13) is a type I cytokeratin that is a marker for mature, non-keratinizing squamous epithelium. KRT13 is found in the suprabasal layers of nonkeratinizing squamous epithelium of the esophagus, larynx, oral cavity, tonsil, and ectocervix, urothelium and respiratory epithelium. Positive staining can also be found in squamous metaplasia, a small percentage of squamous carcinomas (most show reduced expression), urothelial cancers, and Brenner tumors. Mutations are associated with familial White Sponge Nevus, a benign disorder of the oral mucosa. References: J Anat 2009 214(4):516; J Oral Maxillofac Path 201 20(2):300