Primary Ewing sarcoma/peripheral primitive neuroectodermal tumor of the vulva.

We report a case of Ewing sarcoma/peripheral primitive neuroectodermal tumor (ES/pPNET) arising in the vulva in a 17-year-old adolescent girl. Primary extraskeletal ES/pPNET is uncommon and only rarely affects the female genital tract. Characteristic histologic features of ES/pPNET were present in this case including a monomorphic population of small round blue cells with cytoplasmic glycogen confirmed by periodic acid-Schiff and were immunohistochemically positive for CD99 in a membranous and Fli-1 in a nuclear pattern. The presence of an EWS/Fli-1 fusion transcript was demonstrated by reverse transcription polymerase chain reaction and confirmed by direct sequencing. This report described another very rare case of ES/pPNET arising in the vulva and confirmed by molecular analysis.