PATH-92. Redefining a Childhood Ependymoma as MN1-Rearranged Astroblastoma: A Case Report and Literature Review

Astroblastoma is an extremely rare glial tumor with an estimated incidence of less than 1% of primary brain tumors. It predominantly affects young women and is defined by characteristic MN1 rearrangements, most commonly the MN1:BEND2 fusion. Due to its rarity and histologic overlap with other glial neoplasms, accurate diagnosis can be challenging, and limited data exists on optimal management. We present the case of a 14-year-old female with right hemibody muscle spasms who underwent subtotal resection of a left parietal mass with an initial diagnosis of papillary ependymoma. Within 1.5 years, she had recurrent disease for which she underwent gross total resection, and after five years, she received radiation for tumor recurrence. Thirteen years after initial diagnosis, she presented with progressive right-upper-extremity weakness and a transient episode of speech arrest. MRI brain revealed multiple new enhancing masses in the left parietal and frontal lobes. Restaging MRI spine and lumbar puncture demonstrated no metastatic disease. She underwent gross total resection and pathology was consistent with an astroblastoma with high-grade features and the presence of the MN1:BEND2 fusion. The multidisciplinary team elected to defer adjuvant radiation or chemotherapy in favor of serial imaging surveillance. This case raises the possibility of a misdiagnosis in childhood, with the prior lesion potentially representing an astroblastoma rather than a papillary ependymoma. It adds to the paucity of literature on astroblastoma and underscores the importance of molecular diagnostics in distinguishing astroblastoma from histologically similar tumors. We review recent international concerted efforts to molecularly characterize astroblastomas with gene fusions and DNA methylation. Importantly, we emphasize the need for further collaborative studies that are crucial to determine the best clinical management for these rare tumors.