PATH-32. Clinical characteristics and outcome of infratentorial diffuse infiltrating gliomas in adults in the WHO 2021 era

BACKGROUND Infratentorial diffuse infiltrating gliomas are rare in adults and may have distinct clinical behavior compared to supratentorial gliomas. Existing data largely predate the WHO 2021 classification. We aimed to characterize the clinical features and outcomes of pathology-confirmed infratentorial gliomas in adults using updated criteria. METHOD We retrospectively identified 34 adults diagnosed with infratentorial gliomas from 1999 to 2024 at our institution and reclassified tumors using WHO 2021 criteria. Median overall survival (mOS) and progression-free survival (mPFS) were estimated using the Kaplan-Meier method. Prognostic factors were assessed using hazard ratios (HR) in Cox proportional hazards models. RESULTS Median age 32.2 (18.6-77.7). Male to female ratio 1.4. Median KPS at diagnosis 90 (50-100). Common tumor locations included brainstem 19 (55.9%), cerebellum 16 (47.1%), cerebellar peduncle 10 (29.4%), and spinal cord 10 (29.4%). 12 (35.3%) were low-grade glioma (LGG) and 22 (64.7%) were high-grade (HGG). Out of 24 with known IDH status, 2 had canonical and 5 had non-canonical IDH mutations. 19 (55.9%) underwent biopsy and 15 (44.1%) underwent resection. 31 (91.2%) received radiotherapy and 27 (79.4%) received chemotherapy. After a median follow-up of 10.1 years, mOS and mPFS were 16.0 and 6.2 years for LGG; 2.2 and 0.8 years for HGG, respectively. Compared with LGG patients, HGG patients had worse OS (HR: 16.9 (95% CI: 3.71, 76.8), p < 0.001) and PFS (HR: 11.2 (95% CI: 2.30, 54.9), p = 0.003). KPS 90 and above vs. below 90 at diagnosis had better PFS (HR: 0.39 (95% CI: 0.15, 0.99), p = 0.047). Tumor location, biopsy vs. resection and chemotherapy administration were not associated with survival. CONCLUSION In this WHO 2021-reclassified cohort, mOS for HGG was longer than previously reported in infratentorial HGG series. Tumor grade and baseline KPS were the strongest predictors of survival. These findings warrant further validation in larger, multi-institutional cohorts.