Defining an Intermediate-risk Group for Low-grade Glioma: A National Cancer Database Analysis

Background: RTOG 9802 identified a cohort of patients with age less than 40 years and undergoing gross total resection as having low-risk, low-grade glioma (LR-LGG). European Organization for Research and Treatment of Cancer studies have demonstrated additional prognostic features in this group. The aim of this study was to analyze clinical factors associated with overall survival (OS), identify a potentially higher risk group within LR-LGG, and investigate patterns of care for adjuvant therapy.

Materials and methods: Patients with LR-LGG diagnosed between 2010 to 2013 were identified in the National Cancer Database. Kaplan-Meier method was used to analyze OS. Propensity score matching and multivariate analysis were utilized to adjust for differences in cohorts.

Results: A total of 1,032 patients with LR-LGG were identified. Histological breakdown was 42.0% astrocytoma, 33.2% oligodendroglioma, and 25.8% mixed. Median follow-up was 3.9 years; median pre-operative tumor size was 4.0 cm. Overall, 834 (80.8%) underwent observation and 198 (19.2%) received adjuvant therapy. Tumor size >5 cm predicted for receipt of adjuvant therapy on regression analyses (OR=2.02, p=0.001). On multivariate analysis, tumor size >5 cm (hazard ratio=1.95) and non-oligodendroglioma histology (hazard ratio=2.50) were associated with inferior OS (both p<0.05). For patients with both poor prognostic features (a subset we consider "intermediate-risk"), 5-year OS was 78.4%, compared to 94.1% for all other low-risk patients (p<0.001). After propensity score matching, the intermediate-risk group continued to be associated with worse 5-year OS: 80.5% vs. 94.0%, p=0.004.

Conclusion: Due to inferior OS for patients with LR-LGG with >5 cm, non-oligodendroglioma tumors, we propose an 'intermediate-risk' clinical classification for this subset.