title: Epithelioid sarcoma: an immunohistochemical analysis evaluating the utility of cytokeratin 5/6 in distinguishing superficial epithelioid sarcoma from spindled squamous cell carcinoma.
abstract: BACKGROUND
  Epithelioid sarcoma (ES) is a rare, aggressive soft tissue tumor characterized by nodular aggregates of epithelioid and/or spindled cells that are immunoreactive to cytokeratins (CKs) and epithelial membrane antigen. ES that arises in the dermis may cause epidermal ulceration and can resemble, clinically, morphologically and immunohistochemically, cutaneous squamous cell carcinoma. CK 5/6 has recently been found to be an excellent marker of squamous cell carcinoma, including spindled variants, but it is not known if this marker can be utilized to distinguish superficial ES from cutaneous spindled squamous cell carcinoma (SSCC).
  
  
  METHODS
  Twenty-four cases of ES with typical histologic features and 10 cases of SSCC with ultrastructural evidence of epithelial differentiation were studied. Immunohistochemical analysis using an antibody to CK 5/6 was performed. The extent of immunoreactivity was evaluated in a semiquantitative manner using the following scale: 0, < 5% of cells staining; 1+, 6-25% of cells staining; 2+, 26-50% of cells staining; 3+, 51-75% of cells staining; 4+, > 75% of cells staining.
  
  
  RESULTS
  CK 5/6 was expressed in all 10 cases of SSCC, including one case with 3+ staining and six cases with 4+ staining. In contrast, CK 5/6 staining was found only in rare tumor cells (1+ staining) in one of 24 (4%) cases of ES.
  
  
  CONCLUSIONS
  CK 5/6 staining is useful in distinguishing superficial ES from cutaneous SSCC.
authors.affiliation: Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Lin
authors.forename: Marek
authors.initials: M
authors.lastname: Skacel
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Sigel
authors.forename: Wilma F
authors.initials: WF
authors.lastname: Bergfeld
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Montgomery
authors.forename: Cyril
authors.initials: C
authors.lastname: Fisher
authors.forename: John R
authors.initials: JR
authors.lastname: Goldblum
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis*; D002277:Carcinoma / Q000473:pathology; D002294:Carcinoma, Squamous Cell / Q000473:pathology; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D053555:Keratin-5; D007633:Keratins / Q000032:analysis / Q000096:biosynthesis*; D012509:Sarcoma / Q000378:metabolism* / Q000473:pathology; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology
chemical_list: D014408:Biomarkers, Tumor; C503940:KRT5 protein, human; D053555:Keratin-5; D007633:Keratins