EWS Gene Fusions as Diagnostic Markers in Sarcomas: Principles and Guidelines

Highly specrtic chromosomal translocations are found in several primitive sarcomas (1 –3 ). Biologically, the breakpoints of these translocations involve various putative or confirmed transcription factor genes, some of which appear to participate in normal mesenchymal development and differentiation These genes are rearranged by the translocations, resulting in the formation of chimeric genes, encoding novel tumor-specific transcription factors that are presumed to disrupt normal differentiation and lead to sarcomagenesis. Several lines of evidence suggest that the fusion genes encoded by these translocations are likely to be either necessary or sufficient for sarcomagenesis The area has been the subject of several recent reviews (1 –3 ). Besides their biological significance, these translocations are of great diagnostic interest as tumor markers. The morphological diagnosis of sarcomas is often problematic. The possibility of detecting tumor-type-specific translocations represents an extremely useful diagnostic modality The EWS gene, located at 22q12, is the single most commonly involved gene in these translocations and thus plays a pivotal role in several different types of sarcomas, including Ewing’s sarcoma, clear cell sarcoma, desmoplastic small round cell tumor, and extraskeletal myxoid chondrosarcoma (see Table 1 ). We expect that the usefulness of EWS rearrangements as tumor markers in sarcomas will only continue to grow as additional EWS gene fusions are identified.