PL2.2 Pembrolizumab (PEM) in recurrent high-grade glioma (HGG)patients with mismatch repair deficiency (dMMR): an observational study

Abstract

Abstract BACKGROUND Pem, an immune checkpoint inhibitor, demonstrated to be activein various neoplasms with MMRd. No data exists about its efficacy in MMRdglioma patients. MATERIAL AND METHODS MMRd HGG relapsed after receiving RT and CT weretreated with Pem. MMR status was analyzed by immunohistochemistry,including the MLH1, MSH2, MSH6, and PMS2 markers. MMR deficiency wasdefined as presence of a weak (wMMRd) or absent (aMMRd) signal atimmunohistochemistry for at least one MMR protein. Other inclusion criteriawere: ECOG PS 0–2, histologically confirmed gliomas, dexamethasone ≤4 mg.Pem was administrated at 200 mg every 3 weeks until progression disease orunacceptable toxicity. Tumor response was evaluated by brain MRI every 10 weeksaccording to the RANO criteria. OS and PFS were evaluated by Kaplan-Meiercurves. CTCAE v4.0 was used for toxicity. RESULTS among 167 glioma patients, we found 22 MMRd gliomas. 12 PTS were treated with Pem: 8 wMMRd and 4 aMMRd. According to Bethesda criteria, allPTS had microsatellite stability. Tumor histologies included 5 anaplasticastrocytoma, 1 anaplastic oligodendroglioma, 6 glioblastoma (GBM). MSH2deficiency was found in 6 cases, MSH6 deficiency in 9 cases, PMS2 and MLH1deficiency in 2 cases. Median number of prior line of chemotherapy was 1 (range 1–5). Stable disease (SD) was reported in 4 PTS (33%); 8 PTS showedprogressive disease (PD). PTS with anaplastic gliomas showed a statisticallysignificant 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. 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). Grade ≥3 adverse eventswere reported in 8% of PTS. CONCLUSION 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. Analyses for identifying additional molecular predictive factors is ongoing.