Pembrolizumab (Pem) in recurrent high-grade glioma (HGG) patients (PTS) with mismatch repair deficiency (MMRd): An observational study.

Abstract

2043 Background: Pem, an immune checkpoint inhibitor, demonstrated to be active in various neoplasms with MMRd. No data exists about its efficacy in MMRd glioma PTS. Methods: MMRd HGG relapsed after receiving RT and CT were treated with Pem. MMR status was analyzed by immunohistochemistry, including the MLH1, MSH2, MSH6, and PMS2 markers. MMRd was defined as presence of a weak (wMMRd) or absent (aMMRd) signal for at least one MMR protein. Other inclusion criteria were: ECOG PS 0-2, histologically confirmed glioma, dexamethasone ≤4 mg. Pem was administrated at 200 mg every 3 weeks until disease progression or unacceptable toxicity. Tumor response was evaluated by brain MRI every 10 weeks according to the RANO criteria. OS and PFS were evaluated by Kaplan-Meier curves. Results: among 167 glioma PTS, we found 22 MMRd gliomas. 12 PTS were treated with Pem: 8 wMMRd and 4 aMMRd. According to Bethesda criteria, all PTS had microsatellite stability. Tumor histologies included 5 anaplastic astrocytoma, 1 anaplastic oligodendroglioma, 6 glioblastoma (GBM). MSH2 deficiency was found in 6 cases , MSH6 deficiency in 9 cases, PMS2 and MLH1 deficiency in 2 cases. Median number of prior lines of chemotherapy was 1 (range 1-5). Stable disease (SD) was reported in 4 PTS (33%); 8 PTS showed progressive disease (PD). PTS with anaplastic gliomas showed a statistically significant association with SD (p=0.03, OR=3); all GBM PTS reported PD; status of MMRd (weak/absent), IDH (mutated/wild-type), MSH2 and MLH6 (deficient/proficient) were not associated with SD. Median follow up was 14.7 ms. OS was 5.6 ms (95% CI 0.1-13.8), PFS 2.4 ms (95% CI 1.8-2.9). OS was 2.8 ms and 5.6 ms (p=0.9), PFS was 1.8 ms and 3.1 ms (p=0.5) in PTS with wMMRd and aMMRd, respectively. PTS reporting SD and PD had PFS of 7.4 ms (95% CI 4.6-10.2) and 1.8 ms (95% CI 0.2-3.4), p=0.002; OS was “not reached” and 2.8 ms in PTS having SD vs PD (p=0.04), respectively. Grade ≥3 adverse events were reported in 8% of PTS. Conclusions: a subgroup of recurrent MMRd HGG might benefit from Pem, especially anaplastic gliomas. There was a trend for a longer PFS and OS in PTS with aMMRd. The enrollment and analyses for identifying additional molecular predictive factors are ongoing.