Epithelial marker expression does not rule out a diagnosis of Ewing's sarcoma family of tumours.

Epithelial marker expression has been reported in Ewing's sarcoma family of tumors (ESFT). However, cytokeratin (CK), epithelial membrane antigen (EMA), and carcino embryonic antigen (CEA) prevalence has not been assessed thoroughly in a large series of genetically confirmed ESFT. The aim of the present study is to confirm the presence of epithelial markers in a large group of ESFT tested genetically for any of their specific gene fusions and the differential diagnosis with other small round cell tumors. To establish the prevalence of epithelial markers, we then performed immunohistochemical studies with antibodies CK (AE1/AE3), CK8/18, CK34ß12, EMA, E-cadherin, and CEA on 415 genetically confirmed ESFT. Immunoreactivity to cytokeratin, EMA, and CEA was present in 19.2%, 6.6%, and 20.8% of cases, respectively. There was no significant association between epithelial markers and histological subtypes, but the atypical variant of ESFT expressed these markers in a high proportion compared with the peripheral neuroectodermal tumors and the conventional variant. The present findings confirm that epithelial marker expression in ESFT, including EMA and CEA, does not rule out a diagnosis of ESFT, and the integration of clinical, radiological, histopathological, immunohistochemical, and molecular genetic findings should form the basis for the diagnosis of bone and soft tissue sarcomas, especially in tumors with atypical or unusual phenotype.