RNA aggregates harness the danger response for potent cancer immunotherapy.

Cancer immunotherapy remains limited by poor antigenicity and a regulatory tumor microenvironment (TME). Here, we create "onion-like" multi-lamellar RNA lipid particle aggregates (LPAs) to substantially enhance the payload packaging and immunogenicity of tumor mRNA antigens. Unlike current mRNA vaccine designs that rely on payload packaging into nanoparticle cores for Toll-like receptor engagement in immune cells, systemically administered RNA-LPAs activate RIG-I in stromal cells, eliciting massive cytokine/chemokine response and dendritic cell/lymphocyte trafficking that provokes cancer immunogenicity and mediates rejection of both early- and late-stage murine tumor models. In client-owned canines with terminal gliomas, RNA-LPAs improved survivorship and reprogrammed the TME, which became "hot" within days of a single infusion. In a first-in-human trial, RNA-LPAs elicited rapid cytokine/chemokine release, immune activation/trafficking, tissue-confirmed pseudoprogression, and glioma-specific immune responses in glioblastoma patients. These data support RNA-LPAs as a new technology that simultaneously reprograms the TME while eliciting rapid and enduring cancer immunotherapy.

Stroke impact on mortality and psychologic morbidity within the Childhood Cancer Survivor Study.

BACKGROUND: Poor socioeconomic and health-related quality of life (HRQOL) outcomes in survivors of childhood cancer can lead to distress and overall negatively impact the lives of these individuals. The current report has highlighted the impact of stroke and stroke recurrence on mortality, psychological HRQOL, and socioeconomic outcomes within the Childhood Cancer Survivor Study (CCSS). METHODS: The CCSS is a retrospective cohort study with longitudinal follow-up concerning survivors of pediatric cancer who were diagnosed between 1970 and 1986. Mortality rates per 100 person-years were calculated across 3 periods: 1) prior to stroke; 2) after first stroke and before recurrent stroke; and 3) after recurrent stroke. Socioeconomic outcomes, the standardized Brief Symptoms Inventory-18, the Medical Outcomes Study 36-Item Short Form Health Survey, and the CCSS-Neurocognitive Questionnaire also were assessed. RESULTS: Among 14,358 participants (median age, 39.7 years), 224 had a stroke after their cancer diagnosis (single stroke in 161 patients and recurrent stroke in 63 patients). Based on 2636 deaths, all-cause late mortality rates were 0.70 (95% CI, 0.68-0.73) prior to stroke, 1.03 (95% CI, 0.73-1.46) after the first stroke, and 2.42 (95% CI, 1.48-3.94) after the recurrent stroke. Among 7304 survivors, those with stroke were more likely to live with a caregiver (single stroke odds ratio [OR], 2.3 [95% CI, 1.4-3.8]; and recurrent stroke OR, 5.3 [95% CI, 1.7-16.8]) compared with stroke-free survivors. Stroke negatively impacted task efficiency (single stroke OR, 2.4 [95% CI, 1.4-4.1] and recurrent stroke OR, 3.3 [95% CI, 1.1-10.3]) and memory (single stroke OR, 2.1 [95% CI, 1.2-3.7]; and recurrent stroke OR, 3.5 [95% CI, 1.1-10.5]). CONCLUSIONS: Stroke and stroke recurrence are associated with increased mortality and negatively impact HRQOL measures in survivors of pediatric cancer.

Pediatric bithalamic gliomas have a distinct epigenetic signature and frequent EGFR exon 20 insertions resulting in potential sensitivity to targeted kinase inhibition.

Brain tumors are the most common solid tumors of childhood, and the genetic drivers and optimal therapeutic strategies for many of the different subtypes remain unknown. Here, we identify that bithalamic gliomas harbor frequent mutations in the EGFR oncogene, only rare histone H3 mutation (in contrast to their unilateral counterparts), and a distinct genome-wide DNA methylation profile compared to all other glioma subtypes studied to date. These EGFR mutations are either small in-frame insertions within exon 20 (intracellular tyrosine kinase domain) or missense mutations within exon 7 (extracellular ligand-binding domain) that occur in the absence of accompanying gene amplification. We find these EGFR mutations are oncogenic in primary astrocyte models and confer sensitivity to specific tyrosine kinase inhibitors dependent on location within the kinase domain or extracellular domain. We initiated treatment with targeted kinase inhibitors in four children whose tumors harbor EGFR mutations with encouraging results. This study identifies a promising genomically-tailored therapeutic strategy for bithalamic gliomas, a lethal and genetically distinct brain tumor of childhood.

Neurocognitive Outcomes in Children with Brain Tumors.

Brain tumors are the most common solid tumor in childhood, and although survival outcomes continue to improve, survival is frequently offset by devastating late effects from tumor and treatment. The long-term effects of brain tumors and the therapy necessary to treat them range from sensory and neuroendocrine abnormalities to neurocognitive deficits leading to inferior quality of life. The multifactorial neurocognitive injury is one of the most broadly impacting and challenging late effects to predict and subsequently treat. Certain treatment modalities, such as intrathecal methotrexate and radiation, have been shown to be associated with poor neurocognition; however, long-term outcomes remain highly variable. There are efforts underway to investigate how to better predict, identify, and manage such neurocognitive injury in survivors of pediatric brain tumors. Herein, we focus on the current knowledge of neurocognitive outcomes and potential treatment strategies for this high-risk group.

Germline MUTYH Mutation in a Pediatric Cancer Survivor Developing a Secondary Malignancy.

Radiotherapy-induced second malignant neoplasms (SMNs) are a severe late complication in pediatric cancer survivors. Germline mutations in tumor suppressor genes contribute to SMNs; however, the most relevant germline variants mediating susceptibility are not fully defined. The authors performed matched whole-exome sequencing analyses of germline and tumor DNA from 4 pediatric solid tumor survivors who subsequently developed radiation-associated SMNs. Pathogenic and predicted deleterious germline variants were identified for each patient and validated with Sanger sequencing. These germline variants were compared with germline variants in a cohort of 59 pediatric patients diagnosed with primary sarcomas. Pathway analysis was performed to test for similarities in the germline variant profiles between individuals diagnosed with SMNs or primary sarcomas. One index patient was found to have a pathogenic germline monoallelic mutation in the MUTYH gene, which encodes the base excision repair enzyme adenine DNA glycosylase. This specific germline mutation is associated with a form of familial adenomatous polyposis, a new diagnosis in the patient. Germline-level genetic similarity exists between SMN-developing patients and patients developing primary sarcomas, with relevant genes involved in signal transduction and DNA repair mechanisms. The authors identify a germline MUTYH mutation in a pediatric cancer survivor developing an SMN. Germline mutations involving specific pathways such as base excision repair may identify individuals at risk for developing SMNs. The composition of germline variants in individual patients may enable estimates of patient-specific risk for developing SMNs. The authors anticipate that further analyses of germline genomes and epigenomes will reveal diverse genes and mechanisms influencing cancer risk.

A pilot precision medicine trial for children with diffuse intrinsic pontine glioma-PNOC003: A report from the Pacific Pediatric Neuro-Oncology Consortium.

This clinical trial evaluated whether whole exome sequencing (WES) and RNA sequencing (RNAseq) of paired normal and tumor tissues could be incorporated into a personalized treatment plan for newly diagnosed patients (<25 years of age) with diffuse intrinsic pontine glioma (DIPG). Additionally, whole genome sequencing (WGS) was compared to WES to determine if WGS would further inform treatment decisions, and whether circulating tumor DNA (ctDNA) could detect the H3K27M mutation to allow assessment of therapy response. Patients were selected across three Pacific Pediatric Neuro-Oncology Consortium member institutions between September 2014 and January 2016. WES and RNAseq were performed at diagnosis and recurrence when possible in a CLIA-certified laboratory. Patient-derived cell line development was attempted for each subject. Collection of blood for ctDNA was done prior to treatment and with each MRI. A specialized tumor board generated a treatment recommendation including up to four FDA-approved agents based upon the genomic alterations detected. A treatment plan was successfully issued within 21 business days from tissue collection for all 15 subjects, with 14 of the 15 subjects fulfilling the feasibility criteria. WGS results did not significantly deviate from WES-based therapy recommendations; however, WGS data provided further insight into tumor evolution and fidelity of patient-derived cell models. Detection of the H3F3A or HIST1H3B K27M (H3K27M) mutation using ctDNA was successful in 92% of H3K27M mutant cases. A personalized treatment recommendation for DIPG can be rendered within a multicenter setting using comprehensive next-generation sequencing technology in a clinically relevant timeframe.

The genetic landscape of gliomas arising after therapeutic radiation.

Radiotherapy improves survival for common childhood cancers such as medulloblastoma, leukemia, and germ cell tumors. Unfortunately, long-term survivors suffer sequelae that can include secondary neoplasia. Gliomas are common secondary neoplasms after cranial or craniospinal radiation, most often manifesting as high-grade astrocytomas with poor clinical outcomes. Here, we performed genetic profiling on a cohort of 12 gliomas arising after therapeutic radiation to determine their molecular pathogenesis and assess for differences in genomic signature compared to their spontaneous counterparts. We identified a high frequency of TP53 mutations, CDK4 amplification or CDKN2A homozygous deletion, and amplifications or rearrangements involving receptor tyrosine kinase and Ras-Raf-MAP kinase pathway genes including PDGFRA, MET, BRAF, and RRAS2. Notably, all tumors lacked alterations in IDH1, IDH2, H3F3A, HIST1H3B, HIST1H3C, TERT (including promoter region), and PTEN, which genetically define the major subtypes of diffuse gliomas in children and adults. All gliomas in this cohort had very low somatic mutation burden (less than three somatic single nucleotide variants or small indels per Mb). The ten high-grade gliomas demonstrated markedly aneuploid genomes, with significantly increased quantity of intrachromosomal copy number breakpoints and focal amplifications/homozygous deletions compared to spontaneous high-grade gliomas, likely as a result of DNA double-strand breaks induced by gamma radiation. Together, these findings demonstrate a distinct molecular pathogenesis of secondary gliomas arising after radiation therapy and identify a genomic signature that may aid in differentiating these tumors from their spontaneous counterparts.

A systematic review and meta-analysis of outcomes in pediatric, recurrent ependymoma.

PURPOSE: The purpose of this study was to determine outcomes in recurrent pediatric ependymoma. METHODS: We performed a systematic review of PubMed, Embase, Web of Science and the Cochrane Library for studies reporting on survival outcomes for pediatric patients with recurrent ependymoma. We then performed a meta-analysis of all eligible results. Survival outcomes were identified across location of recurrence, therapy at recurrence, and age at recurrence. RESULTS: Eleven studies met final inclusion criteria. Pooled median progression free survival (PFS) from date of first recurrence was 6.7 months (95% confidence interval [95% CI] 4.7-8.8). Pooled median overall survival (OS) from date of first recurrence was 11.2 months (95% CI 6.4-16.0). Participants with supratentorial recurrences demonstrated a shorter OS of 8.3 months (95% CI 3.2-13.3) compared to 20.1 months (95% CI 8.4-31.7) for those with infratentorial recurrence. Patients who underwent surgery at recurrence had a median OS of 24.2 months (95% CI 14.2-34.1) compared to 29.2 months (95% CI 17.4-41.1) in those who received radiation compared to 19.3 months (95% CI 10.3-28.3) in those who received chemotherapy. Patients younger than age 3 years at time of recurrence demonstrated a median OS of 31.0 months (95% CI - 25.3-87.3) compared to 17.5 months (95% CI 9.9-25.2) for those that recurred beyond 3 years of age. CONCLUSIONS: Our findings illustrate that children with recurrent ependymoma suffer from poor outcomes; however, these outcomes range widely depending on patient, tumor, and treatment characteristics. New therapies and treatment strategies are needed to improve outcomes in this group.

Pediatric and adult H3 K27M-mutant diffuse midline glioma treated with the selective DRD2 antagonist ONC201.

BACKGROUND: H3 K27M-mutant diffuse midline glioma is a fatal malignancy with no proven medical therapies. The entity predominantly occurs in children and young adults. ONC201 is a small molecule selective antagonist of dopamine receptor D2/3 (DRD2/3) with an exceptional safety profile. Following up on a durable response in the first H3 K27M-mutant diffuse midline glioma patient who received ONC201 (NCT02525692), an expanded access program was initiated. METHODS: Patients with H3 K27M-mutant gliomas who received at least prior radiation were eligible. Patients with leptomeningeal spread were excluded. All patients received open-label ONC201 orally once every week. Safety, radiographic assessments, and overall survival were regularly assessed at least every 8 weeks by investigators. As of August 2018, a total of 18 patients with H3 K27M-mutant diffuse midline glioma or DIPG were enrolled to single patient expanded access ONC201 protocols. Among the 18 patients: seven adult (> 20 years old) and seven pediatric (< 20 years old) patients initiated ONC201 with recurrent disease and four pediatric patients initiated ONC201 following radiation, but prior to disease recurrence. FINDINGS: Among the 14 patients with recurrent disease prior to initiation of ONC201, median progression-free survival is 14 weeks and median overall survival is 17 weeks. Three adults among the 14 recurrent patients remain on treatment progression-free with a median follow up of 49.6 (range 41-76.1) weeks. Among the 4 pediatric patients who initiated adjuvant ONC201 following radiation, two DIPG patients remain progression-free for at least 53 and 81 weeks. Radiographic regressions, including a complete response, were reported by investigators in a subset of patients with thalamic and pontine gliomas, along with improvements in disease-associated neurological symptoms. INTERPRETATION: The clinical outcomes and radiographic responses in these patients provide the preliminary, and initial clinical proof-of-concept for targeting H3 K27M-mutant diffuse midline glioma with ONC201, regardless of age or location, providing rationale for robust clinical testing of the agent.

Abnormal Morphology of Select Cortical and Subcortical Regions in Neurofibromatosis Type 1.

Purpose To evaluate whether patients with neurofibromatosis type 1 (NF1)-a multisystem neurodevelopmental disorder with myriad imaging manifestations, including focal transient myelin vacuolization within the deep gray nuclei, brainstem, and cerebellum-exhibit differences in cortical and subcortical structures, particularly in subcortical regions where these abnormalities manifest. Materials and Methods In this retrospective study, by using clinically obtained three-dimensional T1-weighted MR images and established image analysis methods, 10 intracranial volume-corrected subcortical and 34 cortical regions of interest (ROIs) were quantitatively assessed in 32 patients with NF1 and 245 age- and sex-matched healthy control subjects. By using linear models, ROI cortical thicknesses and volumes were compared between patients with NF1 and control subjects, as a function of age. With hierarchic cluster analysis and partial correlations, differences in the pattern of association between cortical and subcortical ROI volumes in patients with NF1 and control subjects were also evaluated. Results Patients with NF1 exhibited larger subcortical volumes and thicker cortices of select regions, particularly the hippocampi, amygdalae, cerebellar white matter, ventral diencephalon, thalami, and occipital cortices. For the thalami and pallida and 22 cortical ROIs in patients with NF1, a significant inverse association between volume and age was found, suggesting that volumes decrease with increasing age. Moreover, compared with those in control subjects, ROIs in patients with NF1 exhibited a distinct pattern of clustering and partial correlations. Discussion Neurofibromatosis type 1 is characterized by larger subcortical volumes and thicker cortices of select structures. Most apparent within the hippocampi, amygdalae, cerebellar white matter, ventral diencephalon, thalami and occipital cortices, these neurofibromatosis type 1-associated volumetric changes may, in part, be age dependent. © RSNA, 2018 Online supplemental material is available for this article.

Survival outcomes in pediatric recurrent high-grade glioma: results of a 20-year systematic review and meta-analysis.

Recurrent pediatric high-grade glioma is a leading cause of cancer-related death in children. We report results of a systematic review and meta-analysis investigating survival outcome in pediatric patients with recurrent high-grade glioma over the last 20 years. MEDLINE/PubMed, EMBASE, Web of Science and Cochrane Review databases were searched for relevant studies reporting on survival outcomes for pediatric patients with recurrent high-grade glioma treated between 1996 and 2016. Progression-free survival (PFS) and overall survival (OS) were calculated cumulatively over all studies, by therapy subgroup, and by decade of treatment. Random effects models were used to control for heterogeneity as measured by the I2 statistic. A total of 17 studies across 4 treatment strategies were included. Eleven investigated traditional chemotherapy, 1 investigated targeted therapy, 3 investigated immunotherapy, and 2 investigated radiotherapy. A total of 129 patients were included with a median age of 10.0 years. Cumulative PFS was 3.5 months (95% CI 2.1-5.0). Cumulative OS was 5.6 months (95% CI 3.9-7.3). OS was 4.0 months (95% CI 1.9-6.1) using traditional chemotherapy, 9.3 months using targeted therapies (95% CI 5.4-13), 6.9 months using immunotherapy (95% CI 2.1-12), and 14 months using reirradiation (95% CI 2.8-25). OS between 1996 and 2006 was 4.2 months (95% CI 2.1-6.2) compared to 8.5 months (95% CI 5.6-11) after 2006. Pediatric patients with recurrent high-grade glioma suffer from poor PFS and OS, regardless of therapy. There may be a trend towards improved OS in the last decade.

Reirradiation and PD-1 inhibition with nivolumab for the treatment of recurrent diffuse intrinsic pontine glioma: a single-institution experience.

BACKGROUND: Diffuse intrinsic pontine glioma (DIPG) is a rare, aggressive brain tumor with no known cure. Reirradiation (reRT) at recurrence can prolong survival. The impact of irradiation may be heightened when combined with PD-1 inhibition. We describe our experience using reRT, with or without PD-1 inhibition, in a cohort of patients with recurrent DIPG. METHODS: We performed a retrospective cohort analysis of children who received reRT with or without concomitant PD-1 inhibition for recurrent DIPG at a single institution between 2005 and 2016. We compared progression-free (PFS) and overall survival (OS) between those who received reRT alone or in combination with PD-1 inhibition. We then compared reRT to a cohort of patients who did not receive reRT. RESULTS: Thirty-one patients were included (8-reRT with nivolumab; 4-reRT alone; 19-no reRT). Patients who received reRT had prolonged OS compared to no reRT (22.9 months-reRT with nivolumab; 20.4 months-reRT alone; 8.3 months-no reRT; p < 0.0001). Patients who received reRT with nivolumab vs. reRT only had slightly prolonged OS from diagnosis and from reRT (22.9 vs. 20.4 months for time from diagnosis; 6.8 vs. 6.0 months for time from reRT). All patients receiving reRT with or without nivolumab tolerated the therapy without acute or late toxicity. CONCLUSIONS: Our experience demonstrates the tolerability of reRT with concurrent PD-1 inhibition for recurrent DIPG and suggests that combination therapy may offer survival benefit. Future prospective studies are needed to confirm the benefits of this combination therapy.

Perinatal factors associated with clinical presentation of osteosarcoma in children and adolescents.

BACKGROUND: Osteosarcoma typically develops during puberty with tumors arising at sites of rapid bone growth, suggesting a role for growth-regulating pathways in tumor etiology. Birthweight is one measure of perinatal growth that has been investigated as an osteosarcoma risk factor. Whether birthweight affects clinical features of osteosarcoma remains unexplored. METHOD: Six hundred seventy patients with osteosarcoma, aged 0-19 years, were identified through the California Cancer Registry. We analyzed birth certificate data from the California Department of Public Health vital statistics unit for these patients and 2,860 controls, matched by sex, birth-year, and race/ethnicity. We examined the impact of birthweight on the risk, timing, and clinical presentation of pediatric osteosarcoma including tumor location, size, extension, differentiation, presence of metastasis, and age at onset. Regression models were adjusted for race, sex, gestational age, socioeconomic status, and tumor site. RESULTS: Higher birthweight was associated with more advanced tumor stage (P = 0.017), a trend toward greater tumor extension into surrounding tissues (P = 0.083), and with occurrence of tumors in sites other than the long bones of the arms/legs (P = 9.7 × 10-3 ). Higher birthweight was also associated with an increased likelihood of metastases present at diagnosis (P = 0.047), with each 200 g increase in birthweight associated with a 1.11-fold increase in the odds of having metastatic disease (95% confidence interval: 1.01-1.22). CONCLUSIONS: The association between higher birthweight and more aggressive osteosarcoma, frequently occurring at sites other than the long bones, suggests that growth pathways active during gestation may play an important role in future osteosarcoma progression, especially at anatomic sites with diminished rates of osteoblastic proliferation.

Rational combination platform trial design for children and young adults with diffuse midline glioma: A report from PNOC.

Background Diffuse midline glioma (DMG) is a devastating pediatric brain tumor unresponsive to hundreds of clinical trials. Approximately 80% of DMGs harbor H3K27M oncohistones, which reprogram the epigenome to increase the metabolic profile of the tumor cells. Methods We have previously shown preclinical efficacy of targeting both oxidative phosphorylation and glycolysis through treatment with ONC201, which activates the mitochondrial protease ClpP, and paxalisib, which inhibits PI3K/mTOR, respectively. Results ONC201 and paxalisib combination treatment aimed at inducing metabolic distress led to the design of the first DMG-specific platform trial PNOC022 (NCT05009992). Conclusions Here, we expand on the PNOC022 rationale and discuss various considerations, including liquid biome, microbiome, and genomic biomarkers, quality-of-life endpoints, and novel imaging modalities, such that we offer direction on future clinical trials in DMG.

Clinical trial recruitment of people who speak languages other than english: a children's oncology group report.

BACKGROUND: Persons who speak languages other than English (LOE) are underrepresented in clinical trials; this may be due in part to inadequate multilevel resources. We conducted a survey of institutions affiliated with the Children's Oncology Group (COG) to characterize current research recruitment practices and resources regarding translation and interpretation services. METHODS: In October 2022, a 20-item survey was distributed electronically to institutions affiliated with COG to assess consent practices and resources for recruiting participants who speak LOE to COG trials. Descriptive statistics were used to summarize responses; responses were compared by institution size, type, and respondent role. RESULTS: The survey was sent to a total of 230 institutions, and the response rate was 60% (n = 139). In total, 60% (n = 83) had access to short form consents. Full consent form translation was required at 50% of institutions, and 12% of Institutional Review Boards restricted use of centrally translated consent forms. Forty-six percent of institutions reported insufficient funding to support translation costs; 15% had access to no-cost translation services. Forty-four percent (n = 61) were required to use in-person interpreters for consent discussions; the most cited barrier to obtaining consent was lack of available in-person interpreters (56%). Forty-six percent (n = 69) reported that recruiting persons who speak LOE to clinical trials was somewhat or very difficult. CONCLUSIONS: Institutions affiliated with COG face resource-specific challenges that impede recruitment of participants who speak LOE in clinical trials. These findings indicate an urgent need to identify strategies aimed at reducing recruitment barriers to ensure equitable access to clinical trials.

Safety and pharmacokinetics of ONC201 (dordaviprone) administered two consecutive days per week in pediatric patients with H3 K27M-mutant glioma.

BACKGROUND: This study evaluated the safety and pharmacokinetics (PK) of oral ONC201 administered twice-weekly on consecutive days (D1D2) in pediatric patients with newly diagnosed DIPG and/or recurrent/refractory H3 K27M glioma. METHODS: This phase 1 dose-escalation and expansion study included pediatric patients with H3 K27M-mutant glioma and/or DIPG following ≥1 line of therapy (NCT03416530). ONC201 was administered D1D2 at 3 dose levels (DLs; -1, 1, and 2). The actual administered dose within DLs was dependent on weight. Safety was assessed in all DLs; PK analysis was conducted in DL2. Patients receiving once-weekly ONC201 (D1) served as a PK comparator. RESULTS: Twelve patients received D1D2 ONC201 (DL1, n = 3; DL1, n = 3; DL2, n = 6); no dose-limiting toxicities or grade ≥3 treatment-related adverse events occurred. PK analyses at DL2 (D1-250 mg, n = 3; D1-625 mg, n = 3; D1D2-250 mg, n = 2; D1D2-625 mg, n = 2) demonstrated variability in Cmax, AUC0-24, and AUC0-48, with comparable exposures across weight groups. No accumulation occurred with D1D2 dosing; the majority of ONC201 cleared before administration of the second dose. Cmax was variable between groups but did not appear to increase with D1D2 dosing. AUC0-48 was greater with D1D2 than once-weekly. CONCLUSIONS: ONC201 given D1D2 was well tolerated at all DLs and associated with greater AUC0-48.

Towards Consistency in Pediatric Brain Tumor Measurements: Challenges, Solutions, and the Role of AI-Based Segmentation.

MR imaging is central to the assessment of tumor burden and changes over time in neuro-oncology. Several response assessment guidelines have been set forth by the Response Assessment in Pediatric Neuro-Oncology (RAPNO) working groups in different tumor histologies; however, the visual delineation of tumor components using MRIs is not always straightforward, and complexities not currently addressed by these criteria can introduce inter- and intra-observer variability in manual assessments. Differentiation of non-enhancing tumor from peritumoral edema, mild enhancement from absence of enhancement, and various cystic components can be challenging; particularly given a lack of sufficient and uniform imaging protocols in clinical practice. Automated tumor segmentation with artificial intelligence (AI) may be able to provide more objective delineations, but rely on accurate and consistent training data created manually (ground truth). Herein, this paper reviews existing challenges and potential solutions to identifying and defining subregions of pediatric brain tumors (PBTs) that are not explicitly addressed by current guidelines. The goal is to assert the importance of defining and adopting criteria for addressing these challenges, as it will be critical to achieving standardized tumor measurements and reproducible response assessment in PBTs, ultimately leading to more precise outcome metrics and accurate comparisons among clinical studies.