2001 Evaluating Adjuvant Radiation Therapy for Grade 2 Meningioma: A Multi-Institutional Analysis

INTRODUCTION: Grade 2 meningiomas represent 10-20% of all meningiomas, and there has been intense scrutiny into the efficacy of adjuvant radiation therapy (RT) to reduce progression. METHODS: This was a multi-institutional retrospective cohort study including adult patients with grade 2 meningioma treated at Mass General Brigham hospitals from January 2006 to December 2020. RESULTS: A total of 429 patients with grade 2 meningioma were included (median age 59.7 years,61.5% female). All cases underwent resection, and gross total resection (GTR) was achieved in 298 cases (69.5%). In total, 18.8% cases had adjuvant RT after GTR and 48.9% of cases had adjuvant RT after subtotal resection (STR, though the proportion of patients receiving RT after STR decreased over time. The median follow-up was 5.2 years. Adjuvant RT was not associated with progression-free survival (PFS) after GTR (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). In a subgroup analysis of GTR cases by Simpson grades, there appeared to be a stronger association between adjuvant RT and PFS after Simpson 3 resection (HR 0.49) than after Simpson 2 (HR 0.66) or Simpson 1 (HR 0.89), though these associations were statistically insignificant (p>0.05). Adjuvant RT was associated with improved PFS for cases with Ki67 index equal to or over 10% (HR 1.9; 95% CI 1.05-3.60; p=0.034) but not below 10% (HR 0.9; 95% 0.47-1.67; p=0.93). There were 74 patients (23.9%) who were offered adjuvant RT but did not receive it, and there was no difference in PFS between patients who were offered adjuvant RT and did or did not receive it (p=0.63). CONCLUSIONS: Adjuvant RT for grade 2 meningioma reduced tumor progression after STR, but not GTR.