Pembrolizumab in Treating Younger Patients with Recurrent, Progressive, or Refractory High-Grade Gliomas, Diffuse Intrinsic Pontine Gliomas, Hypermutated Brain Tumors, Ependymoma or Medulloblastoma

Summary

Objectives

PRIMARY OBJECTIVES:
I. To establish the safety and describe adverse effects associated with administration of the adult recommended dose of pembrolizumab (MK-3475) in each stratum separately.
II. To estimate the sustained objective response rate, (complete response [CR] + partial response [PR], sustained for at least 9 weeks) associated with pembrolizumab (MK-3475) treatment for pediatric patients with recurrent, progressive or refractory diffuse intrinsic pontine glioma (DIPG), non-brainstem high grade glioma (NB-HGG), ependymoma or medulloblastoma.
III. To establish the safety and describe adverse effects associated with administration of the adult recommended dose of pembrolizumab (MK-3475) in pediatric patients with progressive or recurrent hypermutated tumors, including those with constitutional mismatch-repair deficiency (CMMRD) syndrome.
IV. To estimate the sustained response rate of pediatric patients with progressive or recurrent hypermutated NB-HGG, including those with CMMRD syndrome, treated with pembrolizumab (MK-3475).
V. To determine changes in the immunophenotypic profile of PD-1hi CD8+ T cells from serial peripheral blood samples obtained before and during treatment with pembrolizumab (MK-3475) in pediatric patients with hypermutated brain tumors, including those with CMMRD syndrome.

SECONDARY OBJECTIVES:
I. To assess the relationship between outcome (response and progression-free survival) and potential biomarkers, including PD-L1 expression, patient immunophenotype, ribonucleic acid (RNA) signature profile, mutational profile, tumor gene expression and circulating tumor deoxyribonucleic acid (DNA) (ctDNA).
II. To estimate the duration of objective response in patients with measurable disease at baseline and estimate progression-free/event-free/overall survival for patients in each stratum treated with pembrolizumab (MK-3475).
III. To evaluate PD-L1 expression on archival tissue obtained from pediatric patients with eligible primary central nervous system (CNS) tumors.
IV. To examine the ability of quantitative magnetic resonance (MR) spectroscopy and diffusion/weighted imaging/apparent diffusion coefficient (ADC) mapping to provide early assessment of tumor behavior and specifically distinguish pseudoprogression/tumor inflammation from tumor progression.
V. To explore the use of serial MR permeability (dynamic contrast-enhanced [DCE]) and MR perfusion (dynamic susceptibility contrast [DSC]) to determine if elevated relative cerebral blood volume (rCBV) and transfer coefficient (ktrans) can distinguish pseudoprogression/tumor inflammation from tumor progression in tumors treated on this protocol.
VI. To characterize biomarkers, patient immunophenotyping, mutational load (as determined by whole exome sequencing), the tumor gene expression profile and ctDNA in patients receiving pembrolizumab (MK-3475).
VII. To estimate the duration of objective response, progression-free survival/event free survival and document overall survival of pediatric patients with progressive or recurrent hypermutated NB-HGG, including those with CMMRD syndrome, treated with pembrolizumab (MK-3475).
VIII. To estimate the progression-free survival (PFS) of all patients enrolled on stratum C and sustained objective response rate of pediatric patients with hypermutated progressive low grade gliomas including those with CMMRD, treated with pembrolizumab (MK-3475).
IX. To categorize the T-cell receptor repertoire in PD-1+ cells obtained from peripheral blood or from tumor tissue, when available, before and after treatment with pembrolizumab (MK-3475) in pediatric patients treated in stratum C (hypermutated brain tumors).
X. To define the specificity of T-cell receptors against tumor antigens identified in objective IX.
XI. To characterize functional features of T-cell populations after pembrolizumab (MK-3475) treatment and relate these findings to epigenetic programs within these cells.

OUTLINE:
Patients receive pembrolizumab intravenously (IV) over 30 minutes on day 1. Treatment repeats every 21 days for 34 cycles in the absence of disease progression or unacceptable toxicity. Patients also undergo standard magnetic resonance imaging (MRI), dynamic contrast-enhanced magnetic resonance (MR) perfusion (DCE permeability) MRI, diffusion tensor imaging (DTI), dynamic susceptibility contrast-perfusion-weighted imaging (DSC perfusion) MRI, diffusion weighted imaging (MR diffusion imaging) and may undergo MR spectroscopy as well as cerebrospinal fluid (CSF) and blood sample collection during screening and on study.

After completion of study treatment, patients are followed up at 30 days, every 3 months for 1 year, then every 6 months for up to 3 years.