SURG-39. LONG-TERM RESULTS OF INTERVENTION FOR GROWING INCIDENTAL MENINGIOMAS OR CONTINUED ACTIVE SURVEILLANCE, A PROSPECTIVE COHORT STUDY

Abstract Incidental meningiomas are common findings. They represent a clinically challenging cohort, without a detailed consensus on their management. The risk of tumor progression and that of intervention must be considered. Long-term prospective data on incidental meningiomas are sparse. We aimed to evaluate the long-term effect of Gamma Knife Radiosurgery (GKRS), surgical resection and continued observation for growing incidental meningiomas. A prospective database of 62 patients (70 tumors) commenced under active surveillance was established in 2009. Radiological and clinical data was obtained until sept 2023. The results of long-term observation (group 1) and intervention with GKRS (group 2) or surgery (group 3) at progression was analyzed. Due to growth, 41 (58.6%) tumors were treated. The mean growth rate was higher prior to GKRS (2.1 cm 3 /y) and surgery (0.4 cm 3 /y) than during long-term active surveillance (0.009 cm 3 /y) (p < 0.001). The meningiomas became in mean 31.3% and 99.1% smaller after GKRS and resection, respectively. In comparison, tumors under long-term surveillance increased in mean 27.2% (p < 0.001). According to the RANO response criteria, the complete, partial, and minimal response versus stable disease rates were higher following intervention, the overall progressive disease rates were similar (Group 1; 20.7%, group 2: 11.4% and group 3: 16.7%) (p = 0.232). Treatment versus no-treatment did not affect overall survival (Group 1; 10.3 y, group 2: 11.8 y and group 3: 13.5 y (p = 0.264). No symptom development was registered in group 1. In group 2, 2.9% experienced transient (grade 2) adverse events, and in group 3, 50% suffered permanent (grade 4) adverse events according to the Common Terminology Criteria for Adverse Events (CTCEAv5). Intervention reduces tumor volume; however, the clinical significance remains uncertain and side effects are not negligible. Active surveillance is safe, saves > 40% of patients from unnecessary interventions and does not compromise future treatments. The optimal timing of intervention should be further explored.