Histopathological features predictive of local control of atypical meningioma after surgery and adjuvant radiotherapy.

OBJECTIVE The goal of this study was to investigate the impact of adjuvant radiotherapy (RT) on local recurrence and overall survival in patients undergoing primary resection of atypical meningioma, and to identify predictive factors to inform patient selection for adjuvant RT. METHODS One hundred eighty-two patients who underwent primary resection of atypical meningioma at a single institution between 1993 and 2014 were retrospectively identified. Patient, meningioma, and treatment data were extracted from the medical record and compared using the Kaplan-Meier method, log-rank tests, multivariate analysis (MVA) Cox proportional hazards models with relative risk (RR), and recursive partitioning analysis. RESULTS The median patient age and imaging follow-up were 57 years (interquartile range [IQR] 45-67 years) and 4.4 years (IQR 1.8-7.5 years), respectively. Gross-total resection (GTR) was achieved in 114 cases (63%), and 42 patients (23%) received adjuvant RT. On MVA, prognostic factors for death from any cause included GTR (RR 0.4, 95% CI 0.1-0.9, p = 0.02) and MIB1 labeling index (LI) ≤ 7% (RR 0.4, 95% CI 0.1-0.9, p = 0.04). Prognostic factors on MVA for local progression included GTR (RR 0.2, 95% CI 0.1-0.5, p = 0.002), adjuvant RT (RR 0.2, 95% CI 0.1-0.4, p < 0.001), MIB1 LI ≤ 7% (RR 0.2, 95% CI 0.1-0.5, p < 0.001), and a remote history of prior cranial RT (RR 5.7, 95% CI 1.3-18.8, p = 0.03). After GTR, adjuvant RT (0 of 10 meningiomas recurred, p = 0.01) and MIB1 LI ≤ 7% (RR 0.1, 95% CI 0.003-0.3, p < 0.001) were predictive for local progression on MVA. After GTR, 2.2% of meningiomas with MIB1 LI ≤ 7% recurred (1 of 45), compared with 38% with MIB1 LI > 7% (13 of 34; p < 0.001). Recursive partitioning analysis confirmed the existence of a cohort of patients at high risk of local progression after GTR without adjuvant RT, with MIB1 LI > 7%, and evidence of brain or bone invasion. After subtotal resection, adjuvant RT (RR 0.2, 95% CI 0.04-0.7, p = 0.009) and ≤ 5 mitoses per 10 hpf (RR 0.1, 95% CI 0.03-0.4, p = 0.002) were predictive on MVA for local progression. CONCLUSIONS Adjuvant RT improves local control of atypical meningioma irrespective of extent of resection. Although independent validation is required, the authors' results suggest that MIB1 LI, the number of mitoses per 10 hpf, and brain or bone invasion may be useful guides to the selection of patients who are most likely to benefit from adjuvant RT after resection of atypical meningioma.