Is the EWS/FLI-1 fusion transcript specific for Ewing sarcoma and peripheral primitive neuroectodermal tumor? A report of four cases showing this transcript in a wider range of tumor types.

Abstract The presence of t(11;22)(q24;q12) is often considered diagnostic of Ewing sarcoma and peripheral primitive neuroectodermal tumor. We report four cases, all of which possessed this translocation as detected by reverse transcriptase polymerase chain reaction and confirmed by sequencing with or without fluorescent in situ hybridization, but none of which were Ewing sarcoma or peripheral primitive neuroectodermal tumor by histological criteria. Two were polyphenotypic tumors and two were mixed embryonal and alveolar rhabdomyosarcomas. Only one case was positive for MIC2 by immunohistochemistry and only in a rare cell. Two cases (one polyphenotypic tumor and one rhabdomyosarcoma) had double minute chromosomes with > 100 copies of the MDM2 gene. The presence of the t(11;22)(q24;ql2) translocation should probably not be considered diagnostic of Ewing sarcoma and peripheral primitive neuroectodermal tumor in the absence of supporting histological evidence. The presence of this translocation in Ewing sarcoma and peripheral primitive neuroectodermal tumor has been taken as evidence that these two tumors are related. Extending this relationship to include some polyphenotypic tumors and some rhabdomyosarcomas may not be justified unless additional evidence is gathered. Pathologists and oncologists will need to decide whether treatment regimens for tumors are better based on phenotype rather than genotype when these two profiles are seemingly in conflict.