Etmr-02. CNS Embryonal Tumor With Brd4–leutx Fusion Potential New Molecular Subtype of Embryonal Tumors in the Future Who Classification of Tumors of the Central Nervous System

Abstract INTRODUCTION Central Nervous System (CNS) embryonal tumors previously called Primitive neuroectodermal tumors of the CNS (CNS-PNETs) are highly malignant tumors that predominantly affect Yonge children. CNS World Health Organization (WHO) 2021classification includes new embryonal tumor subtypes: CNS neuroblastoma, FOXR2-activated, CNS tumor with BCOR internal tandem duplication (ITD), and cribriform neuroepithelial tumor CRINET.CNS-embryonal tumors which cannot be classified into a specific subgroup, considered as ‘‘CNS embryonal tumors, NOS.’’ METHOD We report a 2-year girl previously healthy presented with 2 weeks HX of vomiting, progressive lower limb weakness, and nystagmus. Radiological diagnosis was suggestive of metastatic ATRT with Brain and spine MRI showed a large left interventricular tumor (10.2 x 7.7 x 7.6 cm) centered in the posterior horn of the left lateral ventricle with extensive intracranial and spinal leptomeningeal CSF seeding metastasis she had Partial tumor resection LT-sided external ventricular drain EVD Insertion The tumor showed very aggressive behavior with rapid tumor recurrence/progression post-surgical resection the patient was treated with Palliative chemotherapy due to clinical and neurological deterioration the patient and died 2 months after diagnosis. RESULT Pathological examination showed Embryonal tumor (WHO Grade 4) with Medulloblastoma-like cells Immunohistochemistry: Synaptophysin: Positive Beta-catenin, P53: Negative and INI-1: Retained. NGS molecular testing was positive for BRD4–LEUTX fusion. Tumor DNA- -methylation profiling (DKFZ CNS v12.5) confirmed the diagnosis “CNS embryonal tumor with BRD4–LEUTX fusion” This rare very aggressive/uncurable tumor may show pathological features similarities with Medulloblastoma. Also, BRD4–LEUTX fusion was reported in pediatric epithelioid malignant peripheral nerve sheath tumor and an alveolar rhabdomyosarcoma CONCLUSION CNS tumor with BRD4– LEUTX fusion” A rare tumor has been described in the literatures in infant and young children and may be integrated in the CNS WHO classification as a new highly aggressive subgroup of CNS embryonal tumor.