Exploratory study of PD-1 inhibitors for recurrent meningioma.

26 Background: Meningiomas are the most common primary intracranial tumor. Some patients still have poorly controlled conditions after multiple surgeries and radiotherapies. More effective treatment methods are urgently needed. Previous studies have suggested that meningioma may shape an inhibitory tumor immune microenvironment and achieve immune escape by expressing programmed cell death ligand 1 (PD-L1) and other factors. Immune checkpoint inhibitors (ICIs) such as PD-1 inhibitors have shown promising efficacy in cases, but large-sample studies are needed to confirm these findings. Methods: Recurrent meningioma patients were included and treated with PD-1 inhibitors until tumor progression or intolerance occurred. The efficacy evaluation of enrolled patients used the Response Assessment in Neuro-Oncology (RANO) criteria. The primary endpoint was progression-free survival at 6 months (PFS-6), and secondary endpoints were progression-free survival at 12 months (PFS-12) and overall survival (OS). Adverse events were also recorded. Regular imaging follow-ups were conducted, and clinical characteristics were collected for survival analysis. Peripheral blood lymphocyte subsets and cytokines were detected before and after treatment, and tumor paraffin sections were used for immunohistochemical detection of relevant molecular markers. Results: A total of 35 recurrent meningioma patients (10 grade I, 14 grade II, 11 grade III) were included. Among all grades of patients, the median PFS was 9 months, PFS-6 was 63.6%, and PFS-12 was 47.6%. In grade I patients, the median PFS was 14 months, PFS-6 was 83%, and PFS-12 was 67%. In grade II/III patients, the median PFS was 9 months, PFS-6 was 58.9%, and PFS-12 was 42%. Among all grades of meningioma patients, PFS was significantly correlated with Ki-67 index (P = 0.021) and tumor progression times (P = 0.019). In grade II/III meningioma patients, PFS was only correlated with tumor progression times (P = 0.012). Twenty-five patients had stable disease, and seven patients had disease progression, with no patient achieving partial or complete remission. There was no significant correlation between tumor mutation burden (TMB) and PFS. Further immunohistochemical analysis of tumor tissues in three recurrent high-grade patients revealed varying degrees of increase in local CD3+, CD4+, CD8+ and PD-1+ T lymphocytes after treatment compared to baseline. Conclusions: Our study suggests that PD-1 inhibitors may prolong PFS in recurrent meningioma patients (especially high-grade) with good drug safety, warranting further exploration. Recurrent meningiomas have an immunosuppressive tumor microenvironment, and PD-1 inhibitors may improve the immune status of tumor microenvironments. Clinical trial information: NCT04728568 .