RESUMEN
Hidroacanthoma simplex (HS) is a rare benign intraepidermal tumor thought to originate from the intraepidermal eccrine duct. Many authors regard it as an intraepidermal form of eccrine poroma but there is still a discussion as to the histogenesis of HS. Clinically, it is more common in older adults and affects both sexes equally. It is found more often on the lower extremities and trunk. The clinical appearance is not characteristic, but the lesions are usually flat or slightly elevated verrucous brown plaques. Histopathologically, the tumor shows characteristic intraepidermal nests and is one of a number of cutaneous lesions showing Borst-Jadasshon phenomenon, that is, tendency to form nests within the epidermis. The tumor cells composing nests show a uniform cuboidal appearance and a round, deeply basophilic nucleus typically. The cytoplasm of tumor cell gives a positive PAS reaction that is diastase-labile. We report herein three cases of HS with the results of immunohistochemical studies.