OBJECTIVE Patients with atypical and malignant (WHO Grade II and III)
meningiomas have a worse prognosis than patients with benign (WHO Grade I)
meningiomas. However, there is limited understanding of the pathological risk factors that affect long-term
tumor control following combined treatment with surgery and
radiation therapy. Here, the authors identify clinical and histopathological risk factors for the progression and/or recurrence (P/R) of high-grade
meningiomas based on the largest series of patients with atypical and
malignant meningiomas, as defined by the 2007 WHO classification. METHODS Patients diagnosed with WHO Grade II and III
meningiomas between 2007 and 2014 per the WHO 2007 criteria and treated with both surgery and external beam
radiation therapy were retrospectively reviewed for clinical and histopathological factors at the time of diagnosis and assessed for P/R outcomes at the last available follow-up. RESULTS A total of 76 patients met the inclusion criteria (66 Grade II
meningiomas, 10 Grade III
meningiomas). Median follow-up from the time of pathological diagnosis was 52.6 months. Three factors were found to predict P/R: Grade III histology, brain and/or bone invasion, and a Ki-67 proliferation rate at or above 3%. The crude P/R rate was 80% for patients with Grade III histology, 40% for those with brain and/or bone involvement (regardless of WHO
tumor grade), and 20% for those with a proliferative index ≥ 3% (regardless of WHO
tumor grade). The median proliferation index was significantly different between patients in whom treatment failed and those in whom it did not fail (11% and 1%, respectively). CONCLUSIONS In patients with atypical or
malignant meningiomas, the presence of Grade III histology, brain and/or bone involvement, and a high mitotic index significantly predicted an increased risk of treatment failure despite combination
therapy. These patients can be stratified into risk groups predicting P/R. Patients with high-risk features may benefit from more treatment and counseling than is typically offered currently.