NCOG-21. ADJUVANT RADIATION THERAPY IN ATYPICAL MENINGIOMA TREATMENT DOES NOT IMPROVE PROGRESSION FREE SURVIVAL OR OVERALL SURVIVAL: A RETROSPECTIVE COHORT STUDY

Abstract Treatment of atypical meningiomas (AMs) presents a challenge due to their aggressive nature and tendency to recur. While there is clear evidence for the role of surgical resection of AMs, the use of adjuvant radiation therapy (ART) is a topic of ongoing debate. The aim of this study is to explore the impact of ART following surgical resection of AMs. The primary outcomes of interest are progression free survival (PFS) and overall survival (OS). Records were reviewed for all patients treated for Ams at our institution between January 1, 2014 and January 1, 2024. Patients were grouped into two cohorts, those who were initially treated with surgical resection only and those who also received adjuvant RT. PFS and OS were compared between the two groups using Kaplan Meier curves and Log Rank test. Additionally, multivariable cox proportional hazard models were used to adjust for age, MIB, and resection Simpson grading. There were 76 patients who were initially treated with surgery only and 23 patients who had surgery and ART. No significant difference in PFS or OS was observed between the groups (p=0.3522 and p=0.3636, respectively); including after adjusting for age, MIB, and Simpson grading (HR= 1.55 [0.64-3.76], p= 0.330; and HR = 0.95 [0.31-2.93] p= 0.934, respectively). On multivariate analysis, MIB >10 was associated with a significant difference in PFS (HR=2.76 [1.15-6.59], p=0.023). With ART, PFS was 91% at 12 and 60% at 36 months (versus 89% and 57%, respectively, with surgery only). OS was 95% at 12 and 88% at 36 months (versus 91% and 85%, respectively, with surgery only). In this series, ART was not observed to significantly improve PFS or OS compared to surgery alone. Larger series are needed to determine if there is a subset of patients who benefit from ART.