Comparative Analysis of Routine Histology, Immunohistochemistry, Reverse Transcriptase Polymerase Chain Reaction, and Fluorescence In Situ Hybridization in Diagnosis of Ewing Family of Tumors

Abstract

The Ewing family of tumors are often difficult to distinguish from other malignant small round cell tumors, but more than 90% have EWS-FLI1 chimeric transcript, which acts as a potential molecular diagnostic marker. To do a comparative analysis of 32 cases with EWS-FLI1: Ewing family of tumors (n = 30), desmoplastic small round cell tumor (n = 1), and undifferentiated sarcoma (n = 1). The initial diagnosis was made on core biopsy (n = 22) and open biopsy (n = 4) specimens by using morphology and immunohistochemistry and on fine-needle aspiration cytology ([FNAC], n = 6) specimens. EWS-FLI1 was detected by reverse transcriptase polymerase chain reaction on all 32 fresh FNAC samples and by fluorescence in situ hybridization on 16 paraffin blocks. The 19 male and 13 female patients had bone (n = 19) or soft tissue (n = 13) tumors. Histologic groups were typical Ewing sarcoma (n = 15), atypical Ewing sarcoma (n = 4), Askin Rosai tumors (n = 5), desmoplastic small round cell tumor (n = 1), undifferentiated sarcoma (n = 1), and cases diagnosed as malignant small round cell tumors on FNAC (n = 6). All tumors except desmoplastic small round cell tumor and undifferentiated sarcoma were CD99 positive. EWS-FLI1 by reverse transcriptase polymerase chain reaction was noted in 15 cases of typical Ewing sarcoma, 4 cases of atypical Ewing sarcoma, 5 cases of Askin Rosai tumor, and no cases of desmoplastic small round cell tumor or undifferentiated sarcoma. With use of fluorescence in situ hybridization, EWS break was detected in 10 of 11 paraffin blocks used and was negative in desmoplastic small round cell tumor. The excellent correlation of routine histologic findings in Ewing family of tumors with results on immunohistochemistry and fluorescence in situ hybridization on archival material and reverse transcriptase polymerase chain reaction on fresh FNAC specimens underscores that the traditional observation on routine histologic examination is a time-tested tool. The diagnosis of Ewing family of tumors can be validated on archival material or fresh biopsy samples, including those obtained by FNAC.