KRT6 (Cytokeratin 6, CK6) is a type II cytokeratin protein that along with Keratin 16 or 17, is found in the epidermis of palms, soles, the nail bed, filiform papillae of the tongue, the squamous epithelia of the oral mucosa, tonsil and esophagus, and within hair follicles. It is upregulated in the conjunctiva of patients with Sjogren’s syndrome, as well as in the cornea in keratoconus, and is a marker of hyperproliferating keratinocytes in psoriasis and would healing. Commonly used with Cytokeratin 5, the CK5/6 marker is useful for the identification of mesotheliomas as well as identifying the presence of basal epithelium in benign glands versus malignant prostate and breast carcinomas, where the basal layer is lost. Mutations in KRT6 are associated with a type of pachyonychia congentia. References: Ann NY Acad Sci 2006 1082:56; Dermatol 2000 201:15; J Invest Dermatol 2001 116:330; Histopath 2006 48:223.