Unusual histological variant of Ewing's sarcoma of mandible

Ewing family of tumors (EFTs) comprise highly malignant, nearly undifferentiated neoplasms including Ewing's sarcoma (ES), primitive neuroectodermal tumor (PNET) and a spectrum of other unusual variants. In general, EFTs are included among small blue cell tumors. Establishing histological diagnosis can be difficult; CD99 and FLI1 immunohistochemical staining has improved diagnosis, but these markers are not specific for EFTs. The diagnosis of EFTs is confirmed by molecular diagnostic testing showing the presence of established rearrangements of the EWS gene. The use of this molecular signature in EFTs revealed rare variants in the histomorphologic spectrum of these tumors. The authors report an unusual variant of EFT in the mandible of a 17-year-old patient, which was confirmed by translocation rearrangement in EWR1 gene at 22q12 by fluorescence in situ hybridization. The unusual histologic features, with prominent spindling of tumor cells and deviation from the classic features of Ewing's sarcoma posed a diagnostic challenge for the medical centers involved in the diagnosis and treatment of this patient. This highlights the importance of the genetic study of undifferentiated sarcomas to identify rare morphologic variants of ES, in view of the chemosensitivity of EFTs and how this affects patient management.