Immunostaining of the p30/32MIC2 antigen and molecular detection of EWS rearrangements for the diagnosis of Ewing's sarcoma and peripheral neuroectodermal tumor.

The identification of Ewing's sarcoma (ES) and peripheral neuroectodermal tumor (PNET) among other small round cell tumors (SRCTs) is a critical issue in musculoskeletal pathology because of the lack of clearly distinctive morphological features. In this study, the authors have compared advantages and limits of two procedures that were recently suggested as additional tools for the identification of ES/PNET, the analysis of p30/32MIC2 antigen by immunohistochemistry, and the evaluation of the fusion products of two specific chromosomal aberrations, the t(11;22)(q24;q12) and the t(21;22)(q22;q12), by reverse transcriptase-polymerase chain reaction (RT-PCR). The authors have analyzed the expression of p30/32MIC2 in 28 cell lines and in 90 tumor samples. p30/32MIC2 was highly expressed in ES/PNET but was also present in all the other cell types. The broad spectrum of positivity for p30/32MIC2 in SRCTs of bone was substantially confirmed by the analysis of tissue samples. In the same material, the authors have evaluated the presence of t(11;22) or t(21;22) transcripts (EWS/FLI-1 and EWS/ERG, respectively) by RT-PCR. These transcripts were found in all the cell lines and tissue samples of ES/PNET, but not in other tumors. The authors' results question the use of p30/32MIC2 immunostaining alone for the identification of ES/PNET and suggest the adoption of RT-PCR as an advantageous alternative. Molecular diagnosis of ES/PNET by RT-PCR is highly specific and can be applied to small amounts of tissue. Moreover, RNA extracted from paraffin-embedded specimens was shown to be suitable for RT-PCR analysis, thus enabling analysis of archival material.