Influence of diabetes on survival of patients with glioma: a meta-analysis

Background: The prognostic impact of preexisting diabetes on glioma survival remains unclear, with conflicting evidence across studies. This meta-analysis aimed to assess the association between diabetes and survival outcomes in patients with glioma. Methods: We systematically searched PubMed, Embase, and Web of Science up to April 30, 2025, for cohort studies reporting hazard ratios (HRs) for overall survival (OS) or progression-free survival (PFS) in glioma patients with and without preexisting diabetes. A random-effects model was used to pool multivariate-adjusted HRs accounting for the possible influence of heterogeneity. Results: Twelve retrospective cohort studies comprising 8,948 patients were included. Eleven studies reported on OS, and four on PFS. Pooled analysis showed that preexisting diabetes was associated with poorer OS (HR: 1.22, 95% CI: 1.10-1.36, p < 0.001; I² = 33%). Sensitivity analysis confirmed result robustness (HR range: 1.18-1.26). Subgroup analyses revealed consistent associations regardless of tumor grade (Grade III-IV: HR: 1.42; GBM: HR: 1.19; p for subgroup difference = 0.47), age (< 60 vs. ≥ 60 years, p = 0.15), sex distribution (< 60% vs. ≥ 60% men, p = 0.91), diabetes type (type 2 vs. overall diabetes, p = 0.33), or follow-up duration (≤ 12 vs. >12 months, p = 0.69). Preexisting diabetes was also associated with poorer PFS (HR: 1.36, 95% CI: 1.01-1.83, p = 0.04; I² = 0%). Conclusions: Preexisting diabetes is associated with reduced survival in glioma patients. These findings highlight the importance of integrating metabolic comorbidities into glioma prognostic assessment. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251086248, identifier CRD420251086248.