BACKGROUND: Primitive neuroectodermal tumor/Ewing sarcoma (PNET/EWS) is a round blue cell sarcoma that shows varying degrees of neuroectodermal differentiation. PNET/EWS as a primary intracranial tumor is extremely uncommon.

CASE REPORT: We report a unique case of peripheral PNET presenting as an intracranial mass in an adult following chemotherapy and radiotherapy for a solid tumor. A 51-year-old woman with previously treated left breast cancer was evaluated for a newly developed brain mass. She underwent craniotomy with resection. Surgical pathology was consistent with a peripheral PNET/EWS with Ewing sarcoma gene translocation. She was treated appropriately with vincristine, cyclophosphamide, and doxorubicin (later dactinomycin) alternating with ifosfamide and etoposide.

CONCLUSIONS: Although development of PNET/EWS presenting along the CNS is exceedingly rare in adults, establishing the proper diagnosis of this “small blue cell tumor” is critical. The further distinction between central PNET and peripheral PNET can greatly impact both prognosis and treatment. Our case also highlights the importance of considering the impact of prior intensive therapies, including radiation and chemotherapy, on predisposing to future PNET/EWS.

Keywords: Central Nervous System, Neuroectodermal Tumors, Primitive, Peripheral, Sarcoma, Ewing