3 SUBTYPES OF POROID NEOPLASIA IN A SINGLE LESION - ECCRINE POROMA, HIDROACANTHOMA SIMPLEX, AND DERMAL DUCT TUMOR - HISTOLOGIC, HISTOCHEMICAL, AND ULTRASTRUCTURAL FINDINGS

A single poroid neoplasm composed of three histologically distinct les ions (hidroacanthomas simplex, eccrine poroma, and dermal duct tumor) is reported. Comparative histologic, histochemical, and electron-micro scopic studies revealed that each tumor subtype contained varying prop ortions of poroid cells, clear cells, and cuticular cells. The major c omponent of all three neoplasms was poroid cells, which, under the ele ctron microscope, were characterized by a few, small, poorly developed desmosomes, and were histochemically characterized by a positive succ inic dehydrogenase reaction. The dermal duct tumor was cultured, and s howed similar histochemical findings to the in vivo poroid cells. Thes e results suggest that poroid cells play the most important role in th e histogenesis of these three neoplasms.