Adjuvant radiotherapy for WHO grade II meningiomas: the unanswered question.

Background: WHO grade II meningiomas have a known propensity for recurrence and aggressive clinical behavior. The role of adjuvant radiotherapy after surgical resection remains the subject of ongoing debate, with existing studies showing conflicting conclusions. This study analyzes the impact of adjuvant radiotherapy on progression-free survival (PFS) and cause-specific survival (CSS), focusing on the extent of resection and proliferative index. Methods: We retrospectively analyzed 318 patients with WHO grade II meningiomas treated from 1990 to 2023. All patients underwent surgical resection; 104 received adjuvant radiation therapy. We assessed the survival outcomes using Kaplan-Meier curves and Cox proportional hazards models. Subgroup analyses were performed based on the extent of resection (gross total [GTR] vs. subtotal [STR]) and Ki-67 index (<10% vs. ≥10%). The data were fit to competing risk models by estimating cause-specific hazard functions. Results: At a median follow-up of 5.1 years, adjuvant radiotherapy was associated with significantly reduced PFS after both GTR and STR (p<0.0001) and in both Ki-67 index groups. CSS was also less following radiotherapy after GTR (p=0.0237). Stereotactic fractionated conformal radiotherapy and radiosurgery were independent predictors of recurrence and death. Competing risk models revealed increased hazards of recurrence and mortality across all irradiation modalities. Conclusions: Adjuvant radiotherapy is significantly associated with decreased PFS and CSS, without statistical significance between the GTR and STR groups. In the GTR group, radiation was associated with worse survival outcomes compared to surgery alone. These findings contradict some current treatment paradigms and highlight the urgent need for personalized approaches and further prospective studies with precise parameters to provide a definitive answer.