The prognostic significance of HIST1H3B/C and H3F3A K27M mutations in diffuse midline gliomas is influenced by patient age.

INTRODUCTION: Diffuse midline gliomas (DMGs) are infiltrative midline gliomas harboring H3K27M mutations and are generally associated with poor outcomes. H3K27M mutations include mutations in HIST1H3B/C (H3.1), HIST2H3B/D (H3.2), or H3F3A (H3.3) genes. It is still unclear whether these mutations each portend a universally poor prognosis, or if there are any factors which modulate outcome. The main objective of this study was to study overall survival (OS) of H3.1 versus H3.3 K27M-mutant DMGs in pediatric and adult patients. METHODS: PubMed and Web of Science were searched, and we included studies if they have individual patient data of DMGs with available H3K27M genotype. Kaplan-Meier analysis and Cox regression models were used to analyze the survival of H3.1 and H3.3 mutations in each subgroup. RESULTS: We included 26 studies with 102 and 529 H3.1 and H3.3-mutant DMGs, respectively. The H3.1 mutation was more commonly seen in younger age. In pediatric population, H3.3 mutation conferred a shorter survival (median OS of 10.1 vs 14.2 months; p < 0.001) in comparison to H3.1-positive patients, which was further confirmed in the multivariate Cox analysis. Conversely, H3.3 was associated with a prolonged survival in adult patients as compared with H3.1 mutation (median OS of 14.4 vs 1.7 months; p = 0.019). CONCLUSION: We demonstrated that the prognosis of H3.1 and H3.3 K27M mutation in DMG patients is modulated by patient age. Routine H3K27M mutation genotyping in newly diagnosed DMGs may further stratify patients with these difficult tumors.