Eccrine tubular adenoma--a histopathological, histochemical, and ultrastructural study

A case of eccrine tubular adenoma on the dorsum of the right foot is presented. Histopathologically, in the central nodule of the tumor, the whole dermis was involved and the tumor islands were connected to the epidermis; in the rest of the lesion, tumor islands were observed in the upper dermis. The tumor islands were composed of cystic or alveolar structures and cell masses possessing multiple lumina. Tubules were surrounded by two or more layers of epithelium forming papillations projecting into the lumen. There were only a few basaloid islands and no sclerotic strands. The tumor cells were well differentiated. Acid mucopolysaccharides were seen in the stroma. Histochemically, phosphorylase and acid phosphatase reacted moderately. Succinic dehydrogenase gave a weak reaction and β-glucuronidase was negative in tumor cells. Ultrastructurally, intracellular ducts with numerous microvilli, periluminal filamentous zones, and many multivesicular dense bodies surrounded by a limiting membrane were observed. Keratohyalin granules were absent. Based on these findings, the tumor reported here was considered to be an adenoma differentiating toward the eccrine duct. Some aspects resembled tubular apocrine adenoma, syringoma and basal cell tumor with eccrine differentiation, but they were most similar to papillary eccrine adenoma.