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Meningiomas are the most common primary intracranial tumors. While WHO grade 1 meningiomas can be cured by surgical resection alone, adjuvant radiotherapy (AdjRT) after surgery is recommended in WHO grade 3 (anaplastic). The role of AdjRT for atypical meningiomas (WHO grade 2) is still unclear. This study aims to assess the impact of AdjRT on local control (LC), intracranial progression free survival (PFS) and overall survival (OS) in patients with diagnosis of atypical or anaplastic meningioma.

We retrospectively collected patients with histologically proven newly diagnosed or recurrent WHO grade 2 or 3 meningiomas, who underwent gross total or subtotal resection followed by fractionated AdjRT between 2010 and 2020 at our institution. Response to treatment was evaluated through MRI, according to RECIST criteria. LC, PFS and OS were estimated from the last day of RT using the Kaplan-Meier method and stratified for possible prognostic factors (i.e. RT timing, degree of resection, Ki-67, tumor grading, PTV).

Our retrospective analysis included a total of 92 patients. Of these, 49 were males (53%) and 82 (89%) were diagnosed with an atypical meningioma. In 68 (74%) patients AdjRT was administered upfront following a de-novo diagnosis of meningioma while 24 (26%) patients received AdjRT after re-intervention for disease recurrence following previous surgery. Median age at diagnosis was 62 years. Gross total and subtotal resection was achieved in 58 (63%) and 34 (37%) of patients respectively, with a median Ki-67 of 15%. Median prescribed RT dose was 54 Gy (min 42 Gy, max 60 Gy) administered in daily fractions of 1.8-3 Gy, with a median overall treatment time (OTT) of 44 days. Median PTV volume was 163 cm³. With a median follow-up of 35 months, 3-year LC, PFS and OS were 80%, 73% and 90%, respectively. LC was negatively affected by subtotal resection (p=0.002), Ki-67>15% (p=0.013), high tumor grading (p=0.020) and PTV larger than 165 cm³ (p=0.021). Patients receiving AdjRT after re-intervention had a lower PFS at 3 years compared to those receiving AdjRT upfront after first surgery (82% vs 44%, p=0.003, Figure 1A). Both subtotal resection (p=0.005) and Ki-67>15% (p=0.005) negatively affected PFS. Finally, OS was negatively affected by Ki-67>15% (p=0.031) and by the timing of AdjRT, with patients who underwent upfront AdjRT having a higher OS at 3 years compared to patients receiving delayed AdjRT after re-intervention (96% vs 72% p=0.009, Figure1B).

Upfront adjuvant RT improves PFS and OS at 3 years in patients with WHO grade 2 and 3 meningiomas, whereas no statistically significant difference was identified in terms of LC. Degree of resection, Ki-67, tumor grading and PTV were also found to significantly affect patient outcomes.