CLINICAL AND SURVIVAL OUTCOMES IN ADULT H3 G34 GLIOMA PATIENTS: A RETROSPECTIVE ANALYSIS ACROSS 13 UK CARE CENTRES

Abstract AIMS H3 G34R-mutated gliomas, also known as diffuse hemispheric gliomas, are rare, highly aggressive tumours predominantly affecting children and young adults. In paediatric and adolescent populations, the median time to progression is approximately 10 months, with a median overall survival of 17 months. However, survival outcomes in adult patients remain poorly characterised. This study aims to evaluate the clinical outcomes of adult patients with H3 G34R-mutant gliomas. METHODS We conducted a retrospective cohort study across 13 hospital sites, including patients with molecularly confirmed H3 G34R-mutant gliomas. Data were collected on demographics, tumour location, treatment, histopathology, and clinical outcomes, including overall survival (OS) and progression-free survival (PFS). RESULTS A total of 28 patients were included, 1 of whom were lost to follow-up. Of the remaining 27, The median age at diagnosis was 27.5 years (range: 18–47 years). Most tumours (n=22) were located in the cerebral hemispheres, with the temporal lobe being the most frequently affected region (n=9), followed by the frontal (n=5), parietal (n=4), fronto-parietal (n=3), and fronto-temporal (n=1) lobes. However, not all tumours were confined to a single hemisphere—2 were intraventricular, and 3 exhibited extensive white matter infiltration. The median PFS was 16.2 months (range: 0.8–61.2 months), and the median OS was 18.1 months (range: 0.82–74.3 months). CONCLUSION This study underscores key distinctions between adult and paediatric H3 G34R-mutant gliomas. Notably, not all tumours were confined to a single hemisphere; three cases exhibited diffuse infiltration resembling leukodys- trophy, suggesting a broader anatomical distribution. Over one-third of cases demonstrated overall survival exceeding 24 months, a significantly longer duration than typically expected. Variability in survival outcomes may reflect a rapidly progressive disease course following recurrence, however, this could also be influenced by cohort heterogeneity, follow-up completeness, and potential censorship effects.