Clinically Relevant and Minimally Invasive Tumor Surveillance of Pediatric Diffuse Midline Gliomas Using Patient-Derived Liquid Biopsy

TLDR

Pediatric diffuse midline gliomas are aggressive tumors with poor prognosis, most harboring the H3K27M mutation, and while surgical biopsy is limited, current monitoring relies mainly on imaging, leaving molecular longitudinal assessment largely unexplored. The study aimed to determine whether liquid biopsy could monitor disease response to precision therapy in DMG patients. They developed a droplet digital PCR assay to detect H3K27M and other driver mutations in CSF and plasma from 48 patients (110 samples), enabling longitudinal ctDNA quantification alongside MRI. H3K27M ctDNA was detected in 88% of patients, with CSF being most enriched, and reductions in plasma ctDNA correlated with MRI response in 83% of cases, demonstrating the feasibility and clinical utility of liquid biopsy for longitudinal DMG surveillance.

Abstract

Pediatric diffuse midline glioma (DMG) are highly malignant tumors with poor clinical outcomes. Over 70% of patients with DMG harbor the histone 3 p.K27M (H3K27M) mutation, which correlates with a poorer clinical outcome, and is also used as a criterion for enrollment in clinical trials. Because complete surgical resection of DMG is not an option, biopsy at presentation is feasible, but rebiopsy at time of progression is rare. While imaging and clinical-based disease monitoring is the standard of care, molecular-based longitudinal characterization of these tumors is almost nonexistent. To overcome these hurdles, we examined whether liquid biopsy allows measurement of disease response to precision therapy.We established a sensitive and specific methodology that detects major driver mutations associated with pediatric DMGs using droplet digital PCR (n = 48 subjects, n = 110 specimens). Quantification of circulating tumor DNA (ctDNA) for H3K27M was used for longitudinal assessment of disease response compared with centrally reviewed MRI data.H3K27M was identified in cerebrospinal fluid (CSF) and plasma in 88% of patients with DMG, with CSF being the most enriched for ctDNA. We demonstrated the feasibility of multiplexing for detection of H3K27M, and additional driver mutations in patient's tumor and matched CSF, maximizing the utility of a single source of liquid biome. A significant decrease in H3K27M plasma ctDNA agreed with MRI assessment of tumor response to radiotherapy in 83% (10/12) of patients.Our liquid biopsy approach provides a molecularly based tool for tumor characterization, and is the first to indicate clinical utility of ctDNA for longitudinal surveillance of DMGs.