title: The utility of using immunohistochemistry in the differentiation of metastatic, cutaneous clear cell renal cell carcinoma and clear cell hidradenoma.
abstract: 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 cluster of differentiation marker 10 (CD10) 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 of 12 hidradenomas and 8 of 10 CCRCCs; and highlighted ductal epithelium in 1 of 12 hidradenomas and cystic areas in 4 of 10 CCRCCs. CD10 showed ductal expression in 3 of 12 hidradenomas and membranous staining in 8 of 9 CCRCCs. CEA highlighted ductal epithelium in 11 of 12 hidradenomas while absent in CCRCCs (0/10). Vimentin highlighted neoplastic cells in 8 of 8 CCRCCs and failed to stain the hidradenomas (0/12).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Pathology, Summa Akron City Hospital, Akron, Ohio.
authors.forename: Moises J
authors.identifier: http://orcid.org/0000-0001-7419-1290
authors.initials: MJ
authors.lastname: Velez
authors.affiliation: Department of Pathology, Summa Akron City Hospital, Akron, Ohio.
authors.forename: Courtney L
authors.initials: CL
authors.lastname: Thomas
authors.affiliation: Clinical and Surgical Pathology, Dermatopathology, Regional Medical Laboratory, Tulsa, Oklahoma.
authors.forename: Jason
authors.initials: J
authors.lastname: Stratton
authors.affiliation: Department of Pathology and Dermatopathology, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Wilma
authors.initials: W
authors.lastname: Bergfeld
authors.affiliation: Department of Pathology, Summa Akron City Hospital, Akron, Ohio.
authors.forename: Joshua
authors.initials: J
authors.lastname: Weaver
keywords: PAX-8; clear cell hidradenoma; clear cell renal cell carcinoma; hidradenoma; napsin A; renal cell carcinoma