RARE-50. TREATMENT RESPONSE OF CNS HIGH-GRADE NEUROEPITHELIAL TUMORS WITH MN1 ALTERATION

BACKGROUND: CNS high-grade neuroepithelial tumor with MN1 alteration (CNS HGNET-MN1) are a rare entity recently described as a high-grade tumor containing a mixture of solid and pseudopapillary patterns with MN1 rearrangement. METHODS: CNS HGNET-MN1 patients were identified using genome wide methylation arrays across 5 institutions (the Hospital JP Garrahan, Hospital for Sick Children, the University Hospital Motol, Royal Children`s Hospital and Christchurch Hospital) and was correlated with treatment and outcome. Central imaging review with radiological features analysis was performed. RESULTS: We identified 9 patients harboring CNS HGNET-MN1 tumors through application of the Heidelberg brain tumor classifier. Seven tumors were T supratentorial and two in the spinal cord. Median age was 5 (range 3.6–14.6). All patients had surgery (6 GTR and 3 STR) as initial management followed by radiotherapy (focal 5/CSI 1) and systemic chemotherapy in 2 patients. Four of the 9 patients relapsed by 3 years post diagnosis, with 2 local and 2 metastatic failures despite complete surgical resections and radiotherapy. Three patients died due to tumor relapse after 24 months despite upfront radiotherapy. Seven of 9 patients had an initial diagnosis of ependymoma. CONCLUSION: Treatment of CNS HGNET-MN1 remains a major challenge with multiple failures, despite aggressive surgical resections and upfront involved field radiotherapy. Further multicenter, international prospective studies are required to determine the optimal treatment strategy for this group of tumors.