RARE-10. PRIMARY INTRACRANIAL EWING SARCOMA IN A 12 MONTH OLD MALE

BACKGROUND: Ewing sarcoma (EWS) is a rare type of pediatric bone and soft tissue tumor that accounts for approximately 1% of all pediatric malignancies. It most commonly occurs in the long bones or axial skeleton, and rarely includes extraosseous sites or intracranial involvement. Reports of primary intracranial EWS are minimal. Pediatric intracranial EWS is even more rare with less than 15 cases reported. CASE DESCRIPTION: We describe the case of primary intracranial EWS in a 12 month old male. The patient’s initial MRI showed a large heterogeneous supratentorial cystic and solid mass centered in the right parietal region measuring 9.1cm x10.3cm x 7.6cm. No distant metastases were detected. The patient underwent surgical resection and pathology was consistent with a small round blue cell tumor. Further pathological evaluation revealed presence of EWSR1-FLI1 fusion and was negative for CD99, GFAP, synaptophysin, Olig2, desmin, and CAM5.2. Stains for INI1 and BRG1 were retained. The patient was treated with adjuvant chemotherapy and focal proton beam radiation (as per AEWS0031). CONCLUSION: Primary intracranial Ewing Sarcoma is a rare pediatric brain tumor and, to our knowledge, this would be the youngest reported case to date. This case demonstrates the successful application of a sarcoma-based regimen to a primary intracranial EWS tumor with no evidence of residual tumor on MRI at 8 months into treatment. Future studies should be directed at understanding the biology of these rare tumors and optimizing treatment approaches.