Cytodiagnosis of Extraskeletal Ewing's Sarcoma and its Confirmation by Fluorescence in situ Hybridization.

Extraskeletal Ewing's sarcoma is an aggressive malignant small round cell tumour usually occuring in children and adolescents. It needs to be differentiated from other malignant small round cell tumours and immunohistochemistry plays a pivotal role in establishing the diagnosis. Fluorescence in situ hybridization or real time-polymerase chain reaction helps in confirming the diagnosis by demonstration of EWS-FLI1 translocation, which is found in approximately 85% of the cases. We report a case of extraskeletal Ewing's sarcoma in a10-year-old male, who presented with a right gluteal region mass. Fine needle aspiration and cell block preparation followed by a panel of immunohistochemical markers were performed. Immunohistochemistry for CD99 and FLI1 was positive. EWS-FLI1 translocation was confirmed by fluorescence in situ hybridization.