Immunohistochemistry in the differential diagnosis of nodular hidradenoma and glomus tumor.

The histologic distinction between nodular hidradenoma and glomus tumor is an occasional difficult diagnostic problem. Both tumors may show circumscribed aggregates of uniform epithelioid cells, a myxoid stroma, and variable numbers of blood vessels. Especially troublesome are solid cellular hidradenomas without duct-like structures and glomus tumors without a vascular pattern. To develop an immunohistochemical profile useful in this differential diagnosis, 25 selected skin tumors and four normal glomus bodies were studied with antibodies against low molecular-weight cytokeratin (CAM 5.2), epithelial membrane antigen (EMA), carcino-embryonic antigen (CEA), S-100, and vimentin (VIM). The tumors included eight unequivocal hidradenomas, seven unequivocal glomus tumors, and 10 histologically equivocal cases, originally diagnosed as glomus tumors. In all unequivocal glomus tumors and glomus bodies, only VIM was positive. Of the eight unequivocal hidradenomas, three were positive for CAM 5.2, EMA, CEA, S-100, and VIM; two for CAM 5.2 only; one for CAM 5.2, EMA, and S-100; one for CAM 5.2, EMA, and CEA; and one for CEA only. In the histologically equivocal cases, eight were positive for VIM only, characteristic of glomus tumor; and two were positive for CAM 5.2, EMA, CEA, S-100, and VIM, and were reclassified as hidradenomas. The study suggests that morphologic criteria may not always accurately differentiate between hidradenoma and glomus tumor and that in equivocal cases immunohistochemistry may be useful in the differential diagnosis.