The Utility of Using Immunohistochemistry in the Differentiation of Metastatic, Cutaneous Clear Cell Renal Cell Carcinoma and Clear Cell Hidradenoma.

BACKGROUND: Clear cell hidradenoma and cutaneous clear cell renal cell carcinoma (CCRCC) overlap morphologically. The distinction may be difficult in a patient with a history of CCRCC, presenting with a cutaneous nodule, potentially leading to an erroneous diagnosis. We investigated the usefulness of napsin A and paired box gene 8 (PAX-8) with previously studied markers epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), vimentin and CD 10 in differentiating CCRCC from hidradenoma.

METHODS: We evaluated hidradenomas and cutaneous CCRCCs for immunohistochemical expression of napsin A, PAX-8, EMA, CEA, vimentin, and CD10.

RESULTS: PAX-8 was expressed in all CCRCCs (8/8) while negative in hidradenomas. Napsin A was negative in both hidradenomas (0/12) and CCRCCs (0/10). EMA showed membranous reactivity in 11/12 hidradenomas and 8/10 CCRCCs; and highlighted ductal epithelium in 1/12 hidradenomas and cystic areas in 4/10 CCRCCs. CD10 showed ductal expression in 3/12 hidradenomas and membranous staining in 8/9 CCRCCs. CEA highlighted ductal epithelium in 11/12 hidradenomas while absent in CCRCCs (0/10). Vimentin highlighted neoplastic cells in 8/8 CCRCCs and failed to stain the hidradenomas (0/12).

CONCLUSION: A conservative immunohistochemical panel including PAX-8, vimentin, and CEA allow for easy distinction of CCRCC from hidradenoma, whereas napsin A added no additional value.