Risk Factors for Progression Among Low-Grade Gliomas After Gross Total Resection and Initial Observation in the Molecular Era.

Purpose: To identify risk factors for progression-free survival (PFS) in the molecular era among patients with low-grade glioma (LGG) who undergo gross total resection (GTR) followed by initial observation.

Methods And Materials: We reviewed patients with World Health Organization grade 2 LGG treated at a single institution. We included only those who underwent magnetic resonance imaging (MRI)-confirmed GTR followed by initial observation. Molecular classification was obtained at either the time of diagnosis or pathology review. Cox proportional hazards regression, the Kaplan-Meier method, and the log-rank test were used. P values <.05 were considered statistically significant.

Results: We included 144 patients who underwent MRI-confirmed GTR between 1994 and 2014 followed by initial observation. Median age was 29 years (interquartile range [IQR], 18-41), median tumor size was 2.7 cm (IQR, 1.8-4.0), and median follow-up was 81 months (IQR, 36-132). Molecular classification was 13% IDH-mutant 1p19q-codeleted; 21% IDH-mutant 1p19q-intact; 39% IDH1-R132H-wildtype; and 28% undetermined. For the entire cohort, 5- and 10-year PFS and overall survival were 71% and 53%, and 98% and 90%, respectively. On multivariate analysis, factors associated with worse PFS included increasing age at diagnosis (hazard ratio [HR], 1.05; 95% CI, 1.00-1.09; P = .03), increasing preoperative tumor size (HR, 1.07; 95% CI, 1.04-1.10; P < .0001), and IDH-mutant 1p19q-intact classification (HR, 3.18; 95% CI, 1.15-8.74, P = .025). Median PFS for patients with IDH-mutant 1p19q-codeleted, IDH-mutant 1p19q-intact, and IDH1-R132H-wildtype tumors were 113 months, 56 months, and not reached, respectively. Molecular classification was significantly associated with PFS (P < .0001) but not overall survival (P = .20).

Conclusions: Among patients with LGG who undergo MRI-confirmed GTR and initial observation in the molecular era, increasing age, increasing tumor size, and IDH-mutant 1p19q-intact classification are associated with worse PFS. Because tumor progression is associated with adverse health-related quality of life, these factors may aid clinicians and patients in the shared decision-making process regarding goals of surgery and timing of postoperative therapy. Further study is required to elucidate why IDH-mutant 1p19q-intact LGGs are at higher risk for early progression.