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This research letter discusses a case series of pediatric brain tumors with a specific genetic fusion called MN1::BEND2. The study found that these tumors did not exhibit the typical features of astroblastoma, a type of brain tumor. However, the tumors did show DNA methylation profiles consistent with astroblastoma. The study emphasizes the need for further investigation and optimal treatment for these types of tumors. It also highlights the importance of accurate diagnosis and the need for more research on the clinical responses and long-term outcomes of pediatric patients with MN1-altered tumors. [Extracted from the article]

This study evaluates the diagnostic utility of OLIG2 immunohistochemistry for distinguishing between pediatric high-grade gliomas (pHGG) and embryonal tumors (ETs) of the CNS. Utilizing a retrospective pediatric cohort (1990-2021) of 56 CNS tumors, classified initially as primitive neuroectodermal tumors or CNS ET, we reclassified the cases based on WHO CNS5 criteria after comprehensive review and additional molecular testing that included next-generation sequencing and DNA methylation profiling. Our results indicate that OLIG2 immunopositivity was negative or minimal in a significant subset of pHGG cases (6 out of 11). At the same time, it showed diffuse expression in all cases of CNS neuroblastomas with FOXR2 activation (5/5), demonstrating its limited specificity in differentiating between pHGG and ET. Variable OLIG2 expression in other ETs, ATRT, and ETMR suggests the broader diagnostic implications of the marker. Furthermore, incidental findings of OLIG2 positivity in cases traditionally expected to be negative, such as medulloblastoma and ependymoma, introduce an additional layer of complexity. Together, these findings highlight the challenges of relying solely on OLIG2 immunostaining for accurate tumor classification in pediatric CNS neoplasms and underscore the importance of an integrated diagnostic approach., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Association of Neuropathologists, Inc. All rights reserved. For permissions, please email: journals.permissions@oup.com.)