CNSC-55. THE RARE INTERSECTION OF TRISOMY 21 AND GLIOBLASTOMA IDH WILD-TYPE: A CASE REPORT

Abstract BACKGROUND Primary solid brain tumors, including glioblastomas, are rare in persons with Down syndrome, who are typically more predisposed to hematologic malignancies than solid tumors. The role of trisomy 21 in neuro-oncologic pathophysiology remains poorly understood. We report a rare case of glioblastoma, IDH-wild type, in a young adult with Down syndrome presenting with new-onset focal seizures. CASE DESCRIPTION A 26-year-old male with Down syndrome and no prior neurologic complaints presented with a one-month progression of right temporal headaches, irritability, and behavioral changes, eventually developing focal motor seizures and left-sided hemiparesis. Cranial MRI revealed a mixed cystic solid mass in the right temporal lobe with calcifications and perilesional edema. Electroencephalography showed focal slowing and epileptiform discharges over the right temporal region. The patient underwent craniotomy and safe maximal resection of the tumor. Histopathologic analysis revealed glioblastoma, IDH-wild type. Immunohistochemistry was positive for ATRX, GFAP, OLIG2, and S100, and negative for IDH1, EMA, and CD99. Despite referral to oncology service, the family opted palliative care. The patient was discharged medically stable with outpatient follow-up. DISCUSSION Glioblastoma is exceedingly rare in patients with Down syndrome, possibly due to overexpression of tumor-suppressor genes on chromosome 21. This case highlights the importance of considering structural intracranial pathology in patients with neurodevelopmental disorders who develop new-onset seizures or behavioral decline. Diagnostic delay may occur due to attribution of symptoms to baseline cognitive impairment. Early neurology consult and imaging is critical in such cases. CONCLUSION This case illustrates a highly unusual occurrence of glioblastoma in Down syndrome, a population typically considered at lower risk for solid brain tumors. The importance of clinical vigilance and prompt neuroimaging in patients who present with atypical neurologic symptoms are highlighted here. This case contributes to the sparse literature and raises important questions about tumor pathogenesis in trisomy 21.