Papillary eccrine adenoma. A tubulopapillary hidradenoma with eccrine differentiation.

A slow-growing tumor on the dorsum of the right foot of a 25-year-old female had features that corresponded to papillary eccrine adenoma. The grouping of this entity under the term "tubular apocrine adenoma" in a recent edition of a textbook led to further study of this case in the form of enzyme histochemistry and electron microscopy. The tumor was positive for amylophosphorylase and negative for acid phosphatase, and on electron microscopy showed complex intercellular membrane interdigitation and a possible intercellular canaliculus. No features of apocrine differentiation were found, and we feel that this tumor is distinctly eccrine in its differentiation. The similarity of these two ostensibly separate entities, and the opinion of some authors that intermediate differentiation may be possible in adnexal tumors, would favor them being grouped under the single term of "tubulopapillary hidradenoma," with apocrine or eccrine differentiation as the case may be.