RADT-43. DEVELOPMENT AND VALIDATION OF A PROGNOSTIC NOMOGRAM FOR DIFFUSE MIDLINE GLIOMA: A POPULATION-BASED STUDY

Abstract Diffuse midline glioma (DMG), defined by loss of histone H3 lysine-27 trimethylation (H3K27me3), remains a universally fatal pediatric CNS malignancy with limited therapeutic options. We constructed the largest-to-date prognostic nomogram (n=409) using SEER-22 data (2018–2021), integrating age, tumor location, treatment modality, and socioeconomic status. Our analysis revealed an age-dependent anatomical distribution: brainstem tumors were predominant in children, while adults more commonly presented with non-brainstem disease. Combined chemoradiotherapy (CRT) significantly improved survival (HR=0.41, 95% CI: 0.27–0.63), while chemotherapy alone conferred no benefit. Surgical resection had no impact on survival, consistent with the infiltrative nature of DMG. The nomogram demonstrated moderate discriminative performance (C-index=0.66) and effectively stratified patients into high- and low-risk groups. This model provides a clinically actionable framework for DMG management, supporting risk-adapted strategies: intensified or novel therapies for high-risk patients, and standard CRT for low-risk groups.