Evaluating Adjuvant Radiation Therapy for Grade 2 Meningioma: A Multi-Institutional Analysis.

Background And Objectives: Grade 2 meningiomas are associated with variable rates of local recurrence, and the role of adjuvant radiation therapy (RT) remains debated.

Methods: This was a multi-institutional retrospective cohort study including all adult patients with newly diagnosed and previously untreated grade 2 meningioma treated at Mass General Brigham hospitals from 2006 to 2020. Cox proportional-hazards modeling was used to analyze the impact of adjuvant RT on progression-free survival (PFS).

Results: A total of 429 patients with grade 2 meningioma were included (median age 59.7 years, 61.5% female). Gross total resection (GTR) was achieved in 298 cases (69.5%). Among 284 cases with quantified Ki67 proliferation indices, the median proliferation indice was 10.0% (IQR 6.7%-15%). In total, 18.8% cases had adjuvant RT after GTR and 48.9% of cases had adjuvant RT after subtotal resection (STR). The median follow-up was 5.2 years. Adjuvant RT was not associated with PFS after GTR (hazard ratio [HR] 0.85; 95% CI 0.48-1.52) but was associated with improved PFS after STR (HR 0.54; 95% CI 0.31-0.94). These findings remained consistent after adjusting for age, sex, tumor location, and tumor size. Adjuvant RT was associated with improved PFS for cases with Ki67 index equal to or over 10% (HR 1.89; 95% CI 1.05-3.60; P = .034), but not below 10% (HR 0.94; 95% 0.47-1.67; P = .93).

Conclusion: Adjuvant RT for grade 2 meningioma may reduce tumor progression for patients with Ki67 index ≥10% or after STR and should be considered as part of a multidisciplinary approach to postoperative management. Routine use of adjuvant RT after GTR was not associated with improved PFS, for which avoidance of RT after GTR should be considered to minimize potential treatment-associated morbidity. This study supports selective use of adjuvant RT, optimizing patient outcomes by balancing the benefits of reduced progression against potential morbidities of treatment.