Abstract
A well-demarcated reddish brown elevated plaque appeared on the light pretibial region of a 89-year-old Japanese man. Histologic examinations revealed multiple intraepidermal epitheliomas which could be clearly distinguished from the surrounding keratinocytes. A low power view showed a close resemblance to that of hidroacanthoma simplex. Tumor cells showed a prominent nuclear atypia, and clumping. Individually keratinized cells were also seen in some parts of the tumor nests. Most of the tumor cells were PAS negative. Electron microscopically, the tumor cells showed findings of abnormal keratinization associated with relatively abundant tonofibrils but there were no definite findings indicative of an intraepidermal sweat duct origin.
