CTIM-31. A PHASE II, OPEN-LABEL, SINGLE ARM TRIAL OF PEMBROLIZUMAB FOR REFRACTORY ATYPICAL AND ANAPLASTIC MENINGIOMA AND HEMANGIOPERICYTOMA
Abstract BACKGROUND Grade II and III meningiomas are invasive tumors which tend to recur following initial treatment and are associated with shorter survival (relative to grade I). Hemangiopericytoma (HPC) is a dural based tumor that originates in the pericytes. Treatment options for these tumors include surgical resection and radiation. There are no defined standard treatments after failure these modalities, and effective systemic treatments are lacking. This trial concept was developed following previous reports of high PD-L1 levels in anaplastic meningioma. We currently report our initial experience with pembrolizumab for refractory atypical/anaplastic meningioma (RAM) and HPC patients. METHODS This is a single arm, single institute, phase 2 trial. Inclusion criteria included patients with RAM or HPC whose all previous lines of treatment were exhausted. All patients were treated with pembrolizumab (200mg every 3 weeks) until disease progression. Primary endpoint was 6- and 12-months progression free survival (PFS). The study was planned for 25 patients and we report here preliminary results. RESULTS Through February 2021, 12 patients were enrolled to this study (two with HPC, 10 with RAM). After a median follow up of 18.5 months, the 6 and 12 months PFS were 25% and 16.7% respectively, with a median PFS of 2.75 months. Two patients had a partial response while all others progressed, making the overall response rate 16.7%. One of the responders had HPC and has been stable for 30 months, while the second had atypical meningioma and was stable for 13 months. Median survival has not been reached yet; 1 year survival rate was 82.5%. Grade 3 toxicities included hyperglycemia, elevated liver enzymes and fatigue, with no grade 4 or 5 toxicities. CONCLUSIONS Pembrolizumab induced a low response rate for RAM and HPC. However, a subset of patients might benefit from this treatment with a prolonged response period.