Publication
10015 Background: The gut microbiome exerts a multifaceted influence on treatment outcomes across various cancers, yet its potential role in diffuse midline gliomas (DMGs) remains under-explored. In this report, we present the gut microbiome findings from cohort 2 in the DMG–Adaptive Combination Trial (DMG-ACT, PNOC022). Methods: PNOC022 is an open-label, multi-institutional, international clinical trial using a Bayesian drug combination platform trial design. This report focuses on the combination therapy arm involving dordaviprone and paxalisib, administered to patients (aged 2–39 years) who had completed standard-of-care radiation therapy (Cohort 2). Stool samples were collected at baseline (n = 22), cycle 1 day 1 (n = 15), cycle 7 day 1 (n = 9), and at progression (n = 4). Microbiome profiling was performed with shotgun metagenomic sequencing (NovaSeq X Plus Series, PE150). Progression-free survival (PFS) and overall survival (OS) were analyzed using the Kaplan-Meier method. Longitudinal shifts in microbial communities were evaluated using α-diversity (Shannon-index) and β-diversity (Bray-Curtis dissimilarity index). Baseline α-diversity associations with PFS and OS were examined with log-rank tests and further validated through age-adjusted Cox regression analysis. Results: Between November 2021 and October 2023, 69 biopsy-confirmed DMG patients enrolled (median age 9 years [range 3-37], n = 42 female [61%]) in cohort 2. Median OS from time of diagnosis was 15.6 months (95% CI 12.9-19.5), with a median follow-up time of 19.5 months (95% CI 17.9-23.9). Microbiome analyses were performed for 33 DMG patients (48%). Alpha-diversity and β-diversity remained stable across timepoints. Using baseline samples (n = 22) and a median α-diversity cutoff of the respective group’s values, patients were stratified into two categories (low- vs. high-diversity). Low-diversity was associated with significantly worse PFS and trended worse for OS, resulting in a 6-month PFS: 73% (95%CI 51-100) vs. 100%; p < 0.001) and 12-month OS: 46% (95%CI 24-87) vs. 78% (95%CI 55-100; p = 0.19). Validation using age adjusted Cox regression analysis confirmed a decrease in the risk of progression or death with increasing α-diversity. PFS hazard ratio (HR) was 0.2 (95% CI: 0.1–0.5; p < 0.01) and OS HR was 0.3 (95% CI: 0.1–0.7; p < 0.01). Conclusions: Baseline high alpha-diversity in the gut microbiome is significantly associated with improved PFS and trended towards improved OS in pediatric patients with DMG in cohort 2 of PNOC022. Age-adjusted survival models reinforced its prognostic value for PFS and OS. These findings highlight the potential impact the gut microbiome has on outcomes and will be explored further and warrant our ongoing investigation in PNOC022.