A phase II, open-label, single-arm trial of pembrolizumab for recurrent meningioma and solitary fibrous tumor

Background. Atypical and anaplastic meningiomas account for 20% of all meningioma cases. Solitary fibrous tumor (SFT) is a type of soft tissue sarcoma with similar attributes to meningioma. For patients with refractory or recurrent disease after previous surgery or radiotherapy, there is no effective treatment. Pembrolizumab, an anti-programmed cell death 1 (PD-1) antibody, is an effective treatment for various solid tumors. PD-1 ligand is highly expressed in aggressive meningiomas. We aimed to assess the effectiveness of pembrolizumab in treating meningioma and SFT recurrence after surgery and radiation therapy. Methods. This prospective single-arm phase II trial comprised 15 patients with recurrent meningioma and 3 with anaplastic SFT, treated at a single institution during 2018 to 2022.The study was terminated due to a lack of efficacy and slow accrual.The primary endpoint was 6-month progression-free survival (PFS-6). Results. Median progression-free survival (PFS) was 2.6 months, and median overall survival (OS) was 40 months. The 6- and 12-month PFS were both 11.1%.The 6- and 12-month OS were 94.4% and 61.1%, respectively. According to the Response Assessment in Neuro-Oncology (RANO) criteria, the overall response rate was 11%, with 2 patients achieving stable disease and 2 with partial response.Three patients (16.7%) developed grade 3 toxicity. Conclusions. Our results showed that pembrolizumab failed to improve PFS-6 in patients with aggressive meningioma or anaplastic SFT. However, two patients, one with atypical meningioma and one with anaplastic SFT, achieved a partial response. More clinical studies are needed to identify which subset of patients may benefit from this treatment.