title: The cytology of extraskeletal Ewing sarcoma.
abstract: BACKGROUND
  Extraskeletal Ewing sarcoma (EES) shares histologic, immunohistochemical, and molecular findings with ES of bone. The authors' goal in conducting this study was to examine the cytomorphologic features of EES. In addition, immunocytostaining for CD99/O13 was performed in all cases, and cytogenetic and molecular data were available in about half of the cases.
  
  
  METHODS
  The authors studied 20 aspiration cases, all with histopathologic confirmation, and also conducted immunohistochemistry and/or molecular studies.
  
  
  RESULTS
  All cases had cellular smears with many single cells and focal clustering. Numerous naked nuclei and focal crush artifacts were seen. Mitosis and necrosis were rare. Four cases had cytoplasmic vacuoles. Five cases showed nuclear molding. Seventeen cases (85%) exhibited small cells with scanty cytoplasm and nuclei with fine chromatin and small nucleoli, representing the so-called typical variant. One case (5%) revealed cells with abundant cytoplasm, large nuclei, and large eosinophilic nucleoli, an example of the atypical or large cell variant. Two cases (10%) had features in between, with cells showing a fair amount of cytoplasm and medium-sized nucleoli, representing the intermediate variant. Nuclear grooves, described as common in the latter, were rare. In all cases, in either cytologic or corresponding histologic material, CD99/O13 immunocytostaining showed strong membranous reactivity. In addition, cytogenetic and/or molecular evidence of ES specific chromosomal translocation was demonstrated in histologic or cytologic material in 10 cases.
  
  
  CONCLUSIONS
  EES shows cytologic features similar to ES of bone, with a spectrum of changes ranging from the typical appearance in a majority of cases to intermediate and atypical variants in a minority of cases. CD99/O13 immunocytostaining and/or molecular studies, particularly in the intermediate and atypical variants, may help in establishing a definitive fine-needle aspiration diagnosis, thus avoiding an open surgical biopsy.
authors.affiliation: Cytology Service, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: G E
authors.initials: GE
authors.lastname: Guiter
authors.forename: M M
authors.initials: MM
authors.lastname: Gamboni
authors.forename: M F
authors.initials: MF
authors.lastname: Zakowski
mesh_terms: D000071443:12E7 Antigen; D000293:Adolescent; D000328:Adult; D015703:Antigens, CD / Q000032:analysis; D001707:Biopsy, Needle; D015815:Cell Adhesion Molecules / Q000032:analysis; D002648:Child; D002880:Chromosomes, Human, Pair 11; D002891:Chromosomes, Human, Pair 21; D002892:Chromosomes, Human, Pair 22; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D012512:Sarcoma, Ewing / Q000175:diagnosis / Q000235:genetics / Q000473:pathology*; D012983:Soft Tissue Neoplasms / Q000175:diagnosis / Q000235:genetics / Q000473:pathology*; D014178:Translocation, Genetic
chemical_list: D000071443:12E7 Antigen; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules