Atypical Histopathological Features and the Risk of Treatment Failure in Nonmalignant Meningiomas: A Multi-Institutional Analysis.

Background: Histopathological grading of meningiomas is insufficient for optimal risk stratification. The purpose of the present study was to determine the prognostic value of atypical histopathological features across all nonmalignant meningiomas (World Health Organization [WHO] grade I-II).
Methods: The data from 334 patients with WHO grade I (n = 275) and grade II (n = 59) meningiomas who had undergone surgical resection from 2001 to 2015 at 2 academic centers were pooled. Progression/recurrence (P/R) was determined radiographically and measured from the date of surgery.
Results: The median follow-up was 52 months. The patients were stratified by the number of atypical features: 0 (n = 151), 1 (n = 71), 2 (n = 66), 3 (n = 22), and 4 or 5 (n = 24). The risk of P/R increased with an increasing number of atypical features (log-rank test, P = 0.001). The 5-year actuarial rates of P/R stratified by the number of atypical features were as follows: 0, 16.3% (95% confidence interval [CI], 10.7-24.4); 1, 21.7% (95% CI, 12.8-35.2); 2, 28.2% (95% CI, 18.4-41.7); 3, 30.4% (95% CI, 13.8-58.7); and 4 or 5, 51.4% (95% CI, 31.7-74.5). On univariate analysis, the presence of high nuclear/cytoplasmic ratio (P = 0.007), prominent nucleoli (P = 0.007), and necrosis (P < 0.00005) were associated with an increased risk of P/R. On multivariate analysis, the number of atypical features (hazard ratio [HR], 1.30; 95% CI, 1.03-1.63; P = 0.03), ≥4 mitoses per high-power fields (HR, 2.45; 95% CI, 1.17-5.15; P = 0.02), subtotal resection (HR, 3.9; 95% CI, 2.5-6.3; P < 0.0005), and the lack of adjuvant radiotherapy (HR, 2.40; 95% CI, 1.19-4.80; P = 0.01) were associated with an increased risk of P/R.
Conclusions: An increased number of atypical features, ≥4 mitoses per 10 high-power fields, subtotal resection, and the lack of adjuvant radiotherapy were independently associated with P/R of WHO grade I-II meningiomas. Patients with these features might benefit from intensified therapy.
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