Sinonasal FUS-ERG-Rearranged Ewing's Sarcoma Mimicking Glomangiopericytoma

Ewing's sarcoma is a rare and aggressive tumor that typically arises in the long bones of the extremities. It belongs in the family of small round blue cell tumors and is characterized immunohistochemically by diffuse CD99 expression and molecularly by one of several oncogenic translocations, most commonly t(11;22)(q24;q12) between the EWSR1 gene and the FLI1 gene. Here we present a rare case of Ewing's sarcoma in the sinonasal tract with FUS-ERG gene arrangement that was regarded for almost a decade as a sinonasal-type hemangiopericytoma (glomangiopericytoma). This case illustrates the surprisingly prolonged natural history of Ewing's sarcoma that did not receive therapy for many years and the importance of considering alternative genetic translocations. Our experience suggests that the presence of diffuse CD99 membranous staining pattern in a small blue round cell tumor with morphology typical for Ewing's sarcoma but FISH negative for EWSR1 rearrangement should prompt consideration of FUS-ERG fusion.