IMCT-01: PEMBROLIZUMAB: FIRST EXPERIENCE WITH RECURRENT PRIMARY CENTRAL NERVOUS SYSTEM (CNS) TUMORS

BACKGROUND: Patients with brain tumors that have progressed beyond conventional therapies, and who retain a reasonable functional status are attracted to promising new treatments, even before there is convincing data. Anti-PD1 immunotherapies have been in the spotlight for cancer care since the publication of groundbreaking results for metastatic melanoma with pembrolizumab (PBL). METHODS: We retrospectively reviewed the charts of 17 (12 adults from TASMC and 5 children from SMC) patients with recurrent CNS tumors treated with PBL. We analyzed prior antineoplastic therapies, steroid usage, and outcomes. RESULTS: The group included 17 patients: twelve adults with 9 glioblastomas (GBM), 2 anaplastic astrocytomas (AA), and one brain stem glioma (BSG); and 5 children: 2 BSG; and 1 each of GBM, atypical teratoid/rhabdoid tumor, and medulloblastoma. Patients received anti-neoplastic therapy (average 2 treatment lines; range 1-5) prior to PBL (average 3 infusions, range 1-10). Nine patients started PBL while on steroids (mean dose 4 mg; range 0.5-8) and 3 patients received steroids later during PBL treatment due to clinical deterioration. Eleven patients received concomitant bevacizumab (BVZ) with PBL. All patients showed progressive tumor growth during therapy. One GBM patient underwent tumor resection following 4 cycles of PBL. Histologic examination of tumor-lymphocytic response was unremarkable. There were 2 cases of possible side effects (one with mild rash and increased liver enzymes; and a second case with protracted diarrhea). CONCLUSION: In this retrospective series of 17 heavily-treated patients with recurrent primary CNS tumors, pembrolizumab showed no clinical or radiographic efficacy. While outcomes may have been compromised by the retrospective nature of the study; numerous prior treatments; a mixed population of children and adults; and use of steroids in most of the cases, we do not recommend further use of PBL for recurrent primary CNS tumors unless convincing prospective clinical trial data is published.