Multi-Institutional Study of Stereotactic Radiosurgery for Recurrent WHO Grade 2/3 Meningiomas: An Interim Analysis

Meningiomas are the most common tumors of the central nervous system (CNS). Approximately 80% are classified as World Health Organization (WHO) grade 1, while 20% correspond to grade 2 or grade 3. In those with grade 2/3 disease, local recurrence is not uncommon. Salvage treatment options vary widely and include resection, external beam radiation therapy (EBRT), stereotactic radiosurgery (SRS), and/or clinical trials. Although retrospective studies have reported on the use of upfront SRS in grade 2/3 meningiomas, large-scale outcomes with SRS in the recurrent setting are lacking. The objective of this study was to report on oncologic outcomes for patients with recurrent grade 2/3 meningioma treated with SRS.This is an ongoing multi-institutional retrospective cohort study. Eligibility criteria include patients >18 years old with pathologically confirmed WHO grade 2 or 3 meningioma treated with SRS monotherapy at the time of first recurrence. Patients require pathologic confirmation only at time of diagnosis; those with upfront grade 1 disease must have pathologic confirmation of grade 2/3 disease at time of first recurrence. Patients with multifocal disease upfront were excluded from this study.A total of 60 patients met eligibility criteria. Baseline demographics at time of initial diagnosis are shown in table 1. At the time of first recurrence, 57 (95%) were WHO grade 2, and 3 (5%) were grade 3. Median follow up time from first recurrence was 5.02 years. Median marginal SRS dose was 16 Gy (IQR 14-17) to a 2.67cc planning treatment volume (IQR 1.4-5.1). 92% of patients received single fraction SRS. Median time to second recurrence was 5.92 years. 1, 3, and 5-year progression-free survival (PFS) was 95%, 68%, and 51%, respectively. 1, 3, and 5-year overall survival (OS) was 100%, 98%, and 96%, respectively. On multivariate analysis, grade 3 disease was independently associated with worse PFS (HR 15.7, p = 0.03). Median SRS dose and treatment volume did not correlate with PFS. 1 patient (1.7%) experienced symptomatic radiation necrosis requiring steroids, 3 (5.0%) experienced new seizure activity, and 2 (3.3%) additional patients showed clinical evidence of post-treatment neurocognitive decline.Based on this interim analysis, primary SRS for recurrent grade 2/3 meningioma appears safe and feasible, with outcomes comparable to prospective data on high-risk grade 2/3 patients treated with post-operative fractionated EBRT. We look forward to further analysis with a larger cohort which may help guide further prospective studies.