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2048 Background: Genetic sequencing of diffuse intrinsic pontine glioma (DIPG) and diffuse midline glioma (DMG) biopsy specimens has revealed genomic heterogeneity, fueling an interest in individualized, targeted treatment options. The Pacific Pediatric Neuro-Oncology Consortium recently completed a feasibility study PNOC003: Molecular Profiling for Individualized Treatment Plan for DIPG (NCT02274987), in which a multidisciplinary tumor board recommended targeted agents based on the molecular and genetic profiling of each patient’s tumor. Separately, our group developed a numeric scoring tool of targeted anticancer agents, the Central Nervous System Targeted Agent Prediction (CNS TAP) tool, which combines pre-clinical, clinical, and CNS penetration data with patient-specific genomic information to generate a numeric score for each agent to objectively evaluate these targeted therapies for use in patients with CNS tumors. We hypothesized that highly-scored agents within the CNS-TAP tool would overlap, at least in part, with the agents recommended by the molecular tumor board in PNOC003. Methods: For each study participant (n=28), a retrospective analysis was completed, utilizing the genomic report to identify actionable genetic alterations and to input patient-specific data into CNS TAP to identify the highest scoring agents. We compared high-scoring agents within the CNS TAP tool with recommendations from the PNOC003 tumor board for each of the enrolled 28 patients. Results: Overall, 93% (26/28) of patients had at least one agent recommended by both the tumor board and CNS TAP. Additionally, 39% (37/95) of all agents recommended by the tumor board were also selected by CNS TAP, with additional analysis ongoing. Conclusions: There was significant overlap between the highest-scoring and selected agents via CNS TAP compared with those chose by the molecular tumor board. Through this work, we also identified factors that likely contributed to the discordance in choice of targeted therapies. Without clinician input, the CNS TAP tool is unable to account for drug-drug interactions, includes only designated anticancer agents, and cannot easily be updated in real time, requiring extensive manual literature review for each included agent. However, CNS TAP provides an objective evaluation of targeted therapies, in contrast to inherently subjective recommendations of a tumor board. Given the discordance identified between these methods and the strengths of each, a prospective study incorporating both CNS TAP and a molecular tumor board for targeted therapy selection in patients with high grade glioma is warranted.

2012 Background: Diffuse midline glioma (DMG) with the H3K27M mutation is a lethal childhood brain cancer, with patients rarely surviving 2 years from diagnosis. There are few available means of monitoring the disease beyond serial MRI scans, making clinical decision making slow, difficult, and often reactive. Methods: We conducted a multi-site phase 1 trial of the imipridone ONC201 for children with H3K27M-mutant glioma (NCT03416530). Patients enrolled on Arm D of the trial (n=24) underwent serial lumbar puncture (baseline, 2 and 6 months) for cell-free tumor DNA (cf-tDNA) analysis at time of MRI. Additionally, patients on all arms of the trial at the University of Michigan underwent serial plasma collection. CSF collection was feasible in this cohort, with no procedural complications. We collected a total of 96 plasma samples and 53 CSF samples from 29 patients, including those with H3F3A (H3.3) (n=13), HIST13HB (H3.1) (n= 4), and unknown H3 status/not biopsied (n=12) [range of 0-8 CSF samples and 0-10 plasma samples]. We performed digital droplet polymerase chain reaction (ddPCR) analysis and/or amplicon-based electronic sequencing (Oxford Nanopore) of cf-tDNA samples and compared variant allele fraction (VAF) to radiographic change (maximal 2D tumor area on MRI). Results: Preliminary analysis of samples (n=58) demonstrates a correlation between changes in tumor size and H3K27M cf-tDNA VAF, when removing samples with concurrent bevacizumab. Analysis of remaining CSF and plasma samples is ongoing, including analysis of novel biomarkers of response. In multiple cases, early reduction in CSF cf-tDNA predicts long-term clinical response (>1 year) to ONC201 and does not increase in cases of later-defined pseudo-progression (radiation necrosis). For example, a now 9-year old patient with thalamic H3K27M-mutant DMG underwent treatment with ONC201 after initial radiation and developed an increase in tumor size at 4 months post-radiation (124% baseline) of unclear etiology at the time. Meanwhile, her ddPCR declined from baseline 6.76% VAF to