First Results of the Acsé Pembrolizumab Phase II in the Primary CNS Lymphoma (PCNSL) Cohort

Background: AcSé Pembrolizumab is a Phase 2, open-label, single-arm, multi-cohort, multicentric study investigating the efficacy and safety of pembrolizumab monotherapy in patients with advanced rare cancers (NCT03012620). Here, we report the first results of Pembrolizumab in the cohort of Primary Central Nervous System Lymphoma (PCNSL).

Methods: Main inclusion criteria were: relapsed or refractory PCNSL after one or several lines of treatment including high dose Methotrexate based chemotherapy, pathologically confirmed diffuse large B cell lymphoma, age>18, HIV negative, concurrent steroid medication at a dose no greater than prednisone 20 mg/day or equivalent. Patients received pembrolizumab 200 mg IV as a 30-minute infusion on Day 1 of every 21-day cycles for a maximum of 2 years. The primary endpoint was the confirmed objective response rate according to IPCG at 84 day after the start of treatment. Secondary endpoints included best response (ORR), duration of response, progression-free survival (PFS), overall survival (OS), and safety. Analysis used all enrolled patients.

Results: 50 patients suffering from PCNSL, including 9 primary vitreoretinal lymphoma (PVRL) were included from July, 2017 to October, 2019. Median age was 72 years (range: 43 to 83), Median PS (ECOG) was 1 (range 0-1). The median number of cycles was 4 (range 1-35). At 84 days from start of treatment, 6 patients responded (4 CR+2PR). Overall, 3 patients whose response was not assessed were considered as failures, and the rates of ORR (CR+PR), stable disease (SD), progressive disease (PD) were 26% (13/50, 8 CR + 5 PR), 10% (5/50), 58% (29/50), respectively. ORR was 29% (12/41) and 11% (1/9) in primary cerebral lymphoma and PVRL respectively. After a median follow-up of 6.7 months (range 0.2-27.4), median PFS was 2.6 months, with 6-month PFS of 29.8% and 6-month OS of 60.4%. In responders, median duration of response was estimated at 10 months (95%CI, 2.7 to 12.5). Grade III and IV toxicities related to the drug were observed in 4 patients (8%) and one patient (2%) respectively. No related toxic death was reported.

Conclusion: Pembrolizumab shows moderate activity in relapsed/ refractory PCNSL with acceptable toxicity, supporting further studies evaluating its use in combination therapies.