HGG-23. Prevalence and Prognosis of Infratentorial Spread of Glioblastoma: Two Case Illustrations and Analysis of the Surveillance, Epidemiology, and End Results (SEER) Database

Cerebellar glioblastomas (GBM) originating from the supratentorial space are rare, with limited understanding of their prevalence and prognosis. While GBM is a common aggressive brain tumor, its occurrence in the cerebellum is infrequent and associated with worse outcomes compared to supratentorial GBMs. This study examines the prevalence of cerebellar GBMs spreading from the supratentorial space using the Surveillance Epidemiology and End Results (SEER) database and presents two illustrative cases. Using SEER data (2000–2019), we analyzed the incidence of high-grade gliomas and infratentorial metastatic gliomas localized to the cerebellum. Our search identified 14 patients with infratentorial metastasis of supratentorial gliomas, six of whom had glioblastoma. All glioblastoma patients were over 30 years old. Case 1: A 34-year-old male presented with seizures and was diagnosed with a right temporal GBM (IDH mutant, MGMT methylated). Despite initial treatment, recurrence occurred in the cerebellum, with worsening leptomeningeal disease and hydrocephalus. He passed away 18 months post-diagnosis due to therapy resistance. Case 2: A 20-year-old male presented with a left frontal GBM (IDH wild type, MGMT methylated). Following initial treatment, he developed a cerebellar mass compressing the brainstem. Despite surgery and adjuvant therapy, he succumbed 10 months post-diagnosis due to disease progression. This study highlights the rarity and poor prognosis of cerebellar metastases of supratentorial GBMs. Despite partial tumor resection, chemotherapy, and radiotherapy, cerebellar involvement often signals rapid clinical decline. These findings underscore the need for further investigation into the management and outcomes of such cases.