title: Epithelioid sarcoma: new insights based on an extended immunohistochemical analysis.
abstract: BACKGROUND
  Epithelioid sarcoma has a distinctive epithelioid phenotype and characteristically exhibits immunohistochemical reactivity for epithelial markers (keratins and epithelial membrane antigen) and mesenchymal markers (most notably vimentin and CD34). Antibodies to certain keratin subunits and other novel antigens now available to surgical pathologists have not been tested on a large number of cases.
  
  
  OBJECTIVE
  To assist in the differential diagnosis of epithelioid sarcoma and to help elucidate its histogenesis through an expanded immunohistochemical profile.
  
  
  METHODS
  Immunohistochemical testing with diverse antibodies was performed on 95 archived epithelioid sarcomas including 73 classic and 22 histologically variant subtypes retrieved from the files of the Armed Forces Institute of Pathology.
  
  
  RESULTS
  Immunohistochemical reactivity (number positive/number of cases tested [percent positive], frequency of staining) included keratin 14 (31/64 [48%], variable), gamma-catenin (35/74 [47%], variable), keratin 5/6 (10/33 [30%], focal), calretinin (8/40 [20%], focal), keratin 20 (11/71 [15%], focal), p63 (3/20 [15%], focal), whereas 9 invasive cutaneous squamous cell carcinomas showed strong p63 positivity, epithelial-specific antigen (10/74 [14%], variable), CD117/Kit (5/37 [14%], focal), keratin 15 (3/23 [13%], rare cell), mesothelin (2/64 [3%], rare cell), and CD10 (1/41 [2%], rare cell). No reactivity was observed for keratins 2, 5, and 10.
  
  
  CONCLUSIONS
  Diagnostically, p63 and keratin 5/6 distinguish cutaneous squamous cell carcinoma (positive) from epithelioid sarcoma (usually negative). No single immunomarker was able to distinguish the main 4 histologic subtypes of epithelioid sarcoma, indicating that they are all histogenetically related lesions. The limited expression of specific keratin subtypes used in our study supports the notion that epithelioid sarcoma is a mesenchymal neoplasm capable of partial epithelial transformation.
authors.affiliation: Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Ill, USA. wbl769@northwestern.edu
authors.forename: William B
authors.initials: WB
authors.lastname: Laskin
authors.forename: Markku
authors.initials: M
authors.lastname: Miettinen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D064032:Calbindin 2; D002648:Child; D002675:Child, Preschool; D003598:Cytoskeletal Proteins / Q000032:analysis; D051180:Desmoplakins; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D053547:Keratin-14; D007633:Keratins / Q000032:analysis; D008297:Male; D015260:Neprilysin / Q000032:analysis; D019009:Proto-Oncogene Proteins c-kit / Q000032:analysis; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D012509:Sarcoma / Q000378:metabolism* / Q000473:pathology*; D051185:gamma Catenin
chemical_list: D014408:Biomarkers, Tumor; C576764:CALB2 protein, human; D064032:Calbindin 2; D003598:Cytoskeletal Proteins; D051180:Desmoplakins; C495292:JUP protein, human; C507540:KRT14 protein, human; D053547:Keratin-14; D064030:S100 Calcium Binding Protein G; D051185:gamma Catenin; D007633:Keratins; D019009:Proto-Oncogene Proteins c-kit; D015260:Neprilysin