Immunohistochemical analysis of the mildly hyperplastic “normal” skin of the nude mouse (Fig. 4), compared to trichoblastomas (Fig. 5A–H) and papillomas (Fig. 5I–Q), revealed similar patterns of protein expression for KRT1 and 10 which are normally expressed in the suprabasilar epidermis. The gene discussed is KRT1; the disease is trichoblastoma.