The differential diagnosis of small round cell tumors is exhaustive and requires ancillary studies. Relatively recently, fluorescence in situ hybridization (FISH) using probes for specific gene rearrangements has gained wide acceptance. This technique is particularly useful in the differential diagnosis of Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET) and desmoplastic small round-cell tumor (DSRCT). In ES/PNET, the EWS gene is juxtaposed to the FLI-1 gene in 85% of cases and to the ERG gene in another 7% of cases; the EWS gene is juxtaposed to the WTI gene in DSRCT. Documentation of the EWS gene rearrangements in EWS/PNET has previously been demonstrated in frozen tissue. We report 2 unusual cases of EWS/PNET diagnosed in abdominal tumors in adults. Although the immunohistochemical results supported a diagnosis of ES/PNET, 1 case morphologically resembled DSRCT. The diagnosis in these 2 cases was confirmed by the FISH demonstration of EWS/FLI-1 gene fusion in paraffin-embedded tissue. Thus, the usefulness of FISH demonstration of an EWS gene rearrangement with these specific probes in such unusual cases is supported and is demonstrated in paraffin-embedded tissue.
From the *Division of Hematopathology, Department of Pathology, St. Louis University Health Sciences Center, St. Louis, Missouri; †M. D. Anderson Cancer Center, Houston, Texas; the ‡Department of Pathology and Laboratory Medicine, Children's Hospital, Los Angeles, California; and the §Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Received for publication May 27, 2003; accepted August 20, 2003.
Reprints: Dr. Cherie Dunphy, Division of Hematopathology, Department of Pathology and Laboratory Medicine, CB #7525, Brinkhous-Bullitt Building, University of North Carolina, Chapel Hill, NC 27599-7525 (e-mail: email@example.com).