Tumor mutational burden and driver mutations: Characterizing the genomic landscape of pediatric brain tumors

OV Modulators of the Paediatric Brain TIME: Current Status, Combination Strategies, Limitations and Future Directions

Oncolytic viruses (OVs) are characterised by their preference for infecting and replicating in tumour cells either naturally or after genetic modification, resulting in oncolysis. Furthermore, OVs can elicit both local and systemic anticancer immune responses while specifically infecting and lysing tumour cells. These characteristics render them a promising therapeutic approach for paediatric brain tumours (PBTs). PBTs are frequently marked by a cold tumour immune microenvironment (TIME), which suppresses immunotherapies. Recent preclinical and clinical studies have demonstrated the capability of OVs to induce a proinflammatory immune response, thereby modifying the TIME. In-depth insights into the effect of OVs on different cell types in the TIME may therefore provide a compelling basis for using OVs in combination with other immunotherapy modalities. However, certain limitations persist in our understanding of oncolytic viruses' ability to regulate the TIME to enhance anti-tumour activity. These limitations primarily stem from the translational limitations of model systems, the difficulties associated with tracking reliable markers of efficacy throughout the course of treatment and the role of pre-existing viral immunity. In this review, we describe the different alterations observed in the TIME in PBTs due to OV treatment, combination therapies of OVs with different immunotherapies and the hurdles limiting the development of effective OV therapies while suggesting future directions based on existing evidence.

Intra-tumoral T cells in pediatric brain tumors display clonal expansion and effector properties

Brain tumors in children are a devastating disease in a high proportion of patients. Owing to inconsistent results in clinical trials in unstratified patients, the role of immunotherapy remains unclear. We performed an in-depth survey of the single-cell transcriptomes and clonal relationship of intra-tumoral T cells from children with brain tumors. Our results demonstrate that a large fraction of T cells in the tumor tissue are clonally expanded with the potential to recognize tumor antigens. Such clonally expanded T cells display enrichment of transcripts linked to effector function, tissue residency, immune checkpoints and signatures of neoantigen-specific T cells and immunotherapy response. We identify neoantigens in pediatric brain tumors and show that neoantigen-specific T cell gene signatures are linked to better survival outcomes. Notably, among the patients in our cohort, we observe substantial heterogeneity in the degree of clonal expansion and magnitude of T cell response. Our findings suggest that characterization of intra-tumoral T cell responses may enable selection of patients for immunotherapy, an approach that requires prospective validation in clinical trials.

Immunotherapy for Pediatric Gliomas: CAR-T Cells Against B7H3: A Review of the Literature

BACKGROUND

B7H3 is a co-stimulatory molecule for immune reactions found on the surface of tumor cells in a wide variety of tumors. Preclinical and clinical studies have reported it as a tumor target towards which various immunotherapy modalities could be directed. So far, good results have been obtained in hematological neoplasms; however, a contrasting situation is evident in solid tumors, including those of the CNS, which show high refractoriness to current treatments. The appearance of cellular immunotherapies has transformed oncology due to the reinforcement of the immune response that is compromised in people with cancer.

OBJECTIVE

This article aims to review the literature to describe the advancement in knowledge on B7H3 as a target of CAR-T cells in pediatric gliomas to consider them as an alternative in the treatment of these patients.

RESULTS

Although B7H3 is considered a suitable candidate as a target agent for various immunotherapy techniques, there are still limitations in using CAR-T cells to achieve the desired success.

CONCLUSION

Results obtained with CAR-T cells can be further improved by the suggested proposals; therefore, more clinical trials are needed to study this new therapy in children with gliomas.

Immunobiology and Cytokine Modulation of the Pediatric Brain Tumor Microenvironment: A Scoping Review

Utilizing a Scoping Review strategy in the domain of immune biology to identify immune therapeutic targets, knowledge gaps for implementing immune therapeutic strategies for pediatric brain tumors was assessed. The analysis demonstrated limited efforts to date to characterize and understand the immunological aspects of tumor biology with an over-reliance on observations from the adult glioma population. Foundational knowledge regarding the frequency and ubiquity of immune therapeutic targets is an area of unmet need along with the development of immune-competent pediatric tumor models to test therapeutics and especially combinatorial treatment. Opportunities arise in the evolution of pediatric tumor classification from histological to molecular with targeted immune therapeutics.

Cancer Stem Cells in Tumours of the Central Nervous System in Children: A Comprehensive Review

Cancer stem cells (CSCs) are a subgroup of cells found in various kinds of tumours with stem cell characteristics, such as self-renewal, induced differentiation, and tumourigenicity. The existence of CSCs is regarded as a major source of tumour recurrence, metastasis, and resistance to conventional chemotherapy and radiation treatment. Tumours of the central nervous system (CNS) are the most common solid tumours in children, which have many different types including highly malignant embryonal tumours and midline gliomas, and low-grade gliomas with favourable prognoses. Stem cells from the CNS tumours have been largely found and reported by researchers in the last decade and their roles in tumour biology have been deeply studied. However, the cross-talk of CSCs among different CNS tumour types and their clinical impacts have been rarely discussed. This article comprehensively reviews the achievements in research on CSCs in paediatric CNS tumours. Biological functions, diagnostic values, and therapeutic perspectives are reviewed in detail. Further investigations into CSCs are warranted to improve the clinical practice in treating children with CNS tumours.

Pediatric Brain Tumours: Lessons from the Immune Microenvironment

In spite of recent advances in tumour molecular subtyping, pediatric brain tumours (PBTs) remain the leading cause of cancer-related deaths in children. While some PBTs are treatable with favourable outcomes, recurrent and metastatic disease for certain types of PBTs remains challenging and is often fatal. Tumour immunotherapy has emerged as a hopeful avenue for the treatment of childhood tumours, and recent immunotherapy efforts have been directed towards PBTs. This strategy has the potential to combat otherwise incurable PBTs, while minimizing off-target effects and long-term sequelae. As the infiltration and activation states of immune cells, including tumour-infiltrating lymphocytes and tumour-associated macrophages, are key to shaping responses towards immunotherapy, this review explores the immune landscape of the developing brain and discusses the tumour immune microenvironments of common PBTs, with hopes of conferring insights that may inform future treatment design.

Multi-institution analysis of tumor mutational burden and outcomes in pediatric central nervous system tumor patients

BACKGROUND

Pediatric central nervous system (CNS) tumors are the leading cause of pediatric cancer mortality. Research addressing genomic biomarkers and clinical outcomes is needed to inform therapeutic decision-making.

METHODS

We conducted a retrospective analysis of pediatric patients (age <21) diagnosed with a primary CNS tumor at four upstate New York hospitals from 2008 to 2021. Clinical and histopathologic data were identified from each patient, including genomic analysis of somatic mutations and tumor mutational burden (TMB) where available. These variables were each compared with overall survival using Cox regression analyses. Multivariable analysis was conducted to identify patient characteristics that may independently predict survival.

RESULTS

We identified 119 patients. Common tumor types included low-grade glioma (N = 51), high-grade glioma (N = 29), and medulloblastoma (N = 11). Common driver mutations included TP53 inactivation (N = 16), BRAF-KIAA1549 fusion (N = 16), FGFR1 amplification (N = 12), BRAF V600E mutation (N = 12), NF1 loss (N = 12), and H3F3A K28M mutation (N = 6). Median TMB was one mutation/megabase (mut/Mb, range = 0-132). Overall survival was 79.9%. Variables associated with poorer survival on univariable analysis were higher TMB (p = .002, HR 4.97), high-grade tumors (p = .009, HR 84.3), and high-grade glioma histology (p = .021, HR 3.14). Multivariable analyses further identified TMB (p = .011, HR 4.46) and high-grade histology (p = .015, HR 5.28) as independently predictive of worse survival. Tumor progression was more common in high-TMB (N = 15, 44%) than in low-TMB tumors (N = 19, 35%).

CONCLUSIONS

High TMB is correlated with higher rates of progression and death as compared to low-TMB tumors. These findings may help identify patients who may benefit from alternative treatments, such as immunotherapies.

CAR T-cells to treat brain tumors

Tremendous success using CAR T therapy in hematological malignancies has garnered significant interest in developing such treatments for solid tumors, including brain tumors. This success, however, has yet to be mirrored in solid organ neoplasms. CAR T function has shown limited efficacy against brain tumors due to several factors including the immunosuppressive tumor microenvironment, blood-brain barrier, and tumor-antigen heterogeneity. Despite these considerations, CAR T-cell therapy has the potential to be implemented as a treatment modality for brain tumors. Here, we review adult and pediatric brain tumors, including glioblastoma, diffuse midline gliomas, and medulloblastomas that continue to portend a grim prognosis. We describe insights gained from different preclinical models using CAR T therapy against various brain tumors and results gathered from ongoing clinical trials. Furthermore, we outline the challenges limiting CAR T therapy success against brain tumors and summarize advancements made to overcome these obstacles.

Characteristics of children ≤36 months of age with DIPG: A report from the international DIPG registry

BACKGROUND

Children ≤36 months with diffuse intrinsic pontine glioma (DIPG) have increased long-term survival (LTS, overall survival (OS) ≥24 months). Understanding distinguishing characteristics in this population is critical to improving outcomes.

METHODS

Patients ≤36 months at diagnosis enrolled on the International DIPG Registry (IDIPGR) with central imaging confirmation were included. Presentation, clinical course, imaging, pathology and molecular findings were analyzed.

RESULTS

Among 1183 patients in IDIPGR, 40 were eligible (median age: 29 months). Median OS was 15 months. Twelve patients (30%) were LTS, 3 (7.5%) very long-term survivors ≥5 years. Among 8 untreated patients, median OS was 2 months. Patients enrolled in the registry but excluded from our study by central radiology review or tissue diagnosis had median OS of 7 months. All but 1 LTS received radiation. Among 32 treated patients, 1-, 2-, 3-, and 5-year OS rates were 68.8%, 31.2%, 15.6% and 12.5%, respectively. LTS had longer duration of presenting symptoms (P = .018). No imaging features were predictive of outcome. Tissue and genomic data were available in 18 (45%) and 10 patients, respectively. Among 9 with known H3K27M status, 6 had a mutation.

CONCLUSIONS

Children ≤36 months demonstrated significantly more LTS, with an improved median OS of 15 months; 92% of LTS received radiation. Median OS in untreated children was 2 months, compared to 17 months for treated children. LTS had longer duration of symptoms. Excluded patients demonstrated a lower OS, contradicting the hypothesis that children ≤36 months with DIPG show improved outcomes due to misdiagnosis.

Tumor mutational burden and somatic mutation status to predict disease recurrence in advanced melanoma

Tumor mutational burden (TMB) has recently been identified as a biomarker of response to immune checkpoint inhibitors in many cancers, including melanoma. Co-assessment of TMB with inflammatory markers and genetic mutations may better predict disease outcomes. The goal of this study was to evaluate the potential for TMB and somatic mutations in combination to predict the recurrence of disease in advanced melanoma. A retrospective review of 85 patients with stage III or IV melanoma whose tumors were analyzed by next-generation sequencing was conducted. Fisher's exact test was used to assess differences in TMB category by somatic mutation status as well as recurrence locations. Kaplan-Meier estimates and Cox-proportional regression model were used for survival analyses. The most frequently detected mutations were TERT (32.9%), CDKN2A (28.2%), KMT2 (25.9%), BRAF V600E (24.7%), and NRAS (24.7%). Patients with TMB-L + BRAFWT status were more likely to have a recurrence [hazard ratio (HR), 3.43; confidence interval (CI), 1.29-9.15; P = 0.01] compared to TMB-H + BRAF WT. Patients with TMB-L + NRASmut were more likely to have a recurrence (HR, 5.29; 95% CI, 1.44-19.45; P = 0.01) compared to TMB-H + NRAS WT. TMB-L tumors were associated with local (P = 0.029) and in-transit (P = 0.004) recurrences. Analysis of TMB alone may be insufficient in understanding the relationship between melanoma's molecular profile and the body's immune system. Classification into BRAFmut, NRASmut, and tumor mutational load groups may aid in identifying patients who are more likely to have disease recurrence in advanced melanoma.

Epigenetic mechanisms in paediatric brain tumours: regulators lose control

Epigenetic mechanisms are essential to regulate gene expression during normal development. However, they are often disrupted in pathological conditions including tumours, where they contribute to their formation and maintenance through altered gene expression. In recent years, next generation genomic techniques has allowed a remarkable advancement of our knowledge of the genetic and molecular landscape of paediatric brain tumours and have highlighted epigenetic deregulation as a common hallmark in their pathogenesis. This review describes the main epigenetic dysregulations found in paediatric brain tumours, including at DNA methylation and histone modifications level, in the activity of chromatin-modifying enzymes and in the expression of non-coding RNAs. How these altered processes influence tumour biology and how they can be leveraged to dissect the molecular heterogeneity of these tumours and contribute to their classification is also addressed. Finally, the availability and value of preclinical models as well as the current clinical trials exploring targeting key epigenetic mediators in paediatric brain tumours are discussed.

Targeting tumor microenvironment and metastasis in children with solid tumors

PURPOSE OF REVIEW

The prognosis of pediatric patients with metastatic solid tumors remains poor, necessitating development of novel therapeutic strategies. The biology of the pediatric tumor microenvironment (TME) presents obstacles for the efficacy of current therapeutic approaches including immunotherapies. Targeting various aspects of the TME in pediatric patients with solid tumors represents a therapeutic opportunity that may improve outcomes. Here we will discuss recent advances in characterization of the TME, and clinical advances in targeting the immune, vascular, and stromal aspects of the TME.

RECENT FINDINGS

Although immunotherapies have shown limited success in the treatment of pediatric solid tumor patients thus far, optimization of these approaches to overcome the TME shows promise. In addition, there is increasing focus on the myeloid compartment as a therapeutic target. Vascular endothelial growth factor (VEGF) targeting has resulted in responses in some refractory pediatric solid tumors. There has been relatively little focus on stromal targeting; however, emerging preclinical data are improving our understanding of underlying biology, paving the way for future therapies.

SUMMARY

Although translation of TME-targeting therapies for pediatric solid tumors is in the early stages, we are optimistic that continued exploration of approaches aimed at rebalancing the TME will lead to improved outcomes for this population.

Identification of an Immunogenic Medulloblastoma-Specific Fusion Involving EPC2 and GULP1

Medulloblastoma is the most common malignant brain tumor in children. Immunotherapy is yet to demonstrate dramatic results in medulloblastoma, one reason being the low rate of mutations creating new antigens in this entity. In tumors with low mutational burden, gene fusions may represent a source of tumor-specific neoantigens. Here, we reviewed the landscape of fusions in medulloblastoma and analyzed their predicted immunogenicity. Furthermore, we described a new in-frame fusion protein identified by RNA-Seq. The fusion involved two genes on chromosome 2 coding for the enhancer of polycomb homolog 2 (EPC2) and GULP PTB domain containing engulfment adaptor 1 (GULP1) respectively. By qRT-PCR analysis, the fusion was detected in 3 out of 11 medulloblastoma samples, whereby 2 samples were from the same patients obtained at 2 different time points (initial diagnosis and relapse), but not in other pediatric brain tumor entities. Cloning of the full-length sequence indicated that the fusion protein contains the N-terminal enhancer of polycomb-like domain A (EPcA) of EPC2 and the coiled-coil domain of GULP1. In silico analyses predicted binding of the neoantigen-derived peptide to HLA-A*0201. A total of 50% of the fusions described in the literature were also predicted to produce an immunogenic peptide. The EPC2-GULP1 fusion peptide was able to induce a de novo T cell response characterized by interferon gamma release of CD8⁺ cytotoxic T cells in vitro. While the functional relevance of this fusion in medulloblastoma biology remains to be clarified, our data support an immunotherapeutic approach for pediatric medulloblastoma patients carrying the EPC2-GULP1 fusion and other immunogenic fusions.

The Growing Relevance of Immunoregulation in Pediatric Brain Tumors

Pediatric brain tumors are genetically heterogeneous solid neoplasms. With a prevailing poor prognosis and widespread resistance to conventional multimodal therapy, these aggressive tumors are the leading cause of childhood cancer-related deaths worldwide. Advancement in molecular research revealed their unique genetic and epigenetic characteristics and paved the way for more defined prognostication and targeted therapeutic approaches. Furthermore, uncovering the intratumoral metrics on a single-cell level placed non-malignant cell populations such as innate immune cells into the context of tumor manifestation and progression. Targeting immune cells in pediatric brain tumors entails unique challenges but promising opportunities to improve outcome. Herein, we outline the current understanding of the role of the immune regulation in pediatric brain tumors.

CAR T Cell Therapy's Potential for Pediatric Brain Tumors

Simple Summary

T cells that are genetically engineered to express chimeric antigen receptors constitute an effective new therapy with curative potential for patients with hematological tumors. The value of chimeric antigen receptor T cells in childhood brain tumors, the leading cause of cancer death in children, is less clear. In this context, the main obstacles for these engineered T cells remain how to find them, allow them to infiltrate, and induce them to remain active in the tumor site. Here, we discuss recent progress in the field and examine future directions for realizing the potential of this therapy.

Abstract

Malignant central nervous system tumors are the leading cause of cancer death in children. Progress in high-throughput molecular techniques has increased the molecular understanding of these tumors, but the outcomes are still poor. Even when efficacious, surgery, radiation, and chemotherapy cause neurologic and neurocognitive morbidity. Adoptive cell therapy with autologous CD19 chimeric antigen receptor T cells (CAR T) has demonstrated remarkable remission rates in patients with relapsed refractory B cell malignancies. Unfortunately, tumor heterogeneity, the identification of appropriate target antigens, and location in a growing brain behind the blood–brain barrier within a specific suppressive immune microenvironment restrict the efficacy of this strategy in pediatric neuro-oncology. In addition, the vulnerability of the brain to unrepairable tissue damage raises important safety concerns. Recent preclinical findings, however, have provided a strong rationale for clinical trials of this approach in patients. Here, we examine the most important challenges associated with the development of CAR T cell immunotherapy and further present the latest preclinical strategies intending to optimize genetically engineered T cells’ efficiency and safety in the field of pediatric neuro-oncology.

Rare cases of medulloblastoma with hypermutation

BACKGROUND

Medulloblastoma is the most common malignant brain tumor of childhood and is considered a tumor with low mutational burden (~1 Mut/Mb). Therefore, though the medulloblastoma genomes have been extensively characterized in literature, reports on potential hypermutations and underlying mutagenic processes in medulloblastomas are limited.

AIM

In this report, we studied the landscape of mutational burden in primary and recurrent medulloblastoma. Furthermore, we wanted to understand the differences in underlying mutagenic mechanisms in medulloblastoma with low and high mutational burdens.

METHODS

Fifty-three primary and recurrent medulloblastoma genomic sequence were downloaded from the European Genome Archive as BAM files. Thirty-three cases were obtained from formalin-fixed paraffin-embedded tissues from pathology diagnostic archives of Spectrum Health and Cooperative Human Tissue Network. Somatic mutations were called using Mutect2, following best practices guidelines for Genome Analysis Toolkit V4. Mutational signatures were analyzed using deconstructSigs.

RESULTS

We identified nine medulloblastoma cases with high mutational burden (>5 Mut/Mb). Of them, five cases met the criteria of hypermutation (>10Mut/Mb), two of the five tumors had canonical mutations in the POLE proof-reading domain, where a large proportion of mutations in these tumor genomes contributed to signature 10. The hypermutated cases also demonstrated mutational signatures 14, 15, and 21, indicating the role of mis match repair deficiency in their mutagenesis. Of the four known molecular subgroups in medulloblastoma-SHH, WNT, Group 3, and Group 4-both the POLE-mutated cases belonged to the SHH subgroup. This report identifies rare cases of hypermutation in medulloblastoma driven by defects in DNA repair mechanisms.

CONCLUSION

Hypermutation in medulloblastoma can impact therapeutic decisions, especially at recurrence in otherwise fatal high risk SHH-medulloblastomas. A defect in DNA repair leading to SHH -medulloblastoma is yet another important mechanism that should be further investigated in the genesis of these tumors. Therefore, this report provides important scientific and clinical rationale for future research looking for incidence of hypermutation in large cohorts of medulloblastoma patients.

Association of HMGA2 Polymorphisms with Glioma Susceptibility in Chinese Children

Background

Glioma is a malignant central nervous system tumor in children, with poor outcomes and prognosis. HMGA2 is a proto-oncogene with increased expression in various malignancies.

Methods

We explored the association of HMGA2 polymorphisms with glioma susceptibility in Chinese children using a case-control study (191 cases, 248 controls). HMGA2 single nucleotide polymorphisms (rs6581658 A>G; rs8756 A>C; rs968697 T>C) were genotyped using PCR-based TaqMan.

Results

Increased glioma susceptibility was associated with rs6581658 A>G; AG (adjusted odds ratio (OR) = 1.71, 95% confidence interval (CI) = 1.13–2.58, P = 0.010) or GG (adjusted OR = 3.12, 95% CI = 1.26–7.74, P = 0.014) genotype carriers had significantly raised glioma risk compared with AA genotype carriers. The rs6581658 AG/GG (adjusted OR = 1.85, 95% CI = 1.25–2.73, P = 0.002) and AA/GG (adjusted OR = 2.58, 95% CI = 1.05–6.33, P = 0.038) genotypes were associated with an increased risk of glioma relative to the AA genotype. Subjects with 2–3 risk genotypes had a significantly elevated risk (adjusted OR = 1.93, 95% CI = 1.31–2.84, P = 0.001) relative to those with 0–1 risk genotype.

Conclusion

HMGA2 rs6581658 A>G is associated with glioma susceptibility in Chinese children.

Veliparib Is an Effective Radiosensitizing Agent in a Preclinical Model of Medulloblastoma

Medulloblastoma is the most common malignant childhood brain tumor, and 5-year overall survival rates are as low as 40% depending on molecular subtype, with new therapies critically important. As radiotherapy and chemotherapy act through the induction of DNA damage, the sensitization of cancer cells through the inhibition of DNA damage repair pathways is a potential therapeutic strategy. The poly-(ADP-ribose) polymerase (PARP) inhibitor veliparib was assessed for its ability to augment the cellular response to radiation-induced DNA damage in human medulloblastoma cells. DNA repair following irradiation was assessed using the alkaline comet assay, with veliparib inhibiting the rate of DNA repair. Veliparib treatment also increased the number of γH2AX foci in cells treated with radiation, and analysis of downstream pathways indicated persistent activation of the DNA damage response pathway. Clonogenicity assays demonstrated that veliparib effectively inhibited the colony-forming capacity of medulloblastoma cells, both as a single agent and in combination with irradiation. These data were then validated in vivo using an orthotopic implant model of medulloblastoma. Mice harboring intracranial D425 medulloblastoma xenografts were treated with vehicle, veliparib, 18 Gy multifractionated craniospinal irradiation (CSI), or veliparib combined with 18 Gy CSI. Animals treated with combination therapy exhibited reduced tumor growth rates concomitant with increased intra-tumoral apoptosis observed by immunohistochemistry. Kaplan–Meier analyses revealed a statistically significant increase in survival with combination therapy compared to CSI alone. In summary, PARP inhibition enhanced radiation-induced cytotoxicity of medulloblastoma cells; thus, veliparib or other brain-penetrant PARP inhibitors are potential radiosensitizing agents for the treatment of medulloblastoma.

Predicting clinical outcomes using cancer progression associated signatures

Somatic mutation signatures are an informative facet of cancer aetiology, however they are rarely useful for predicting patient outcome. The aim of this study is to evaluate the utility of a panel of 142 mutation-signature–associated metrics (P142) for predicting cancer progression in patients from a ‘TCGA PanCancer Atlas’ cohort. The P142 metrics are comprised of AID/APOBEC and ADAR deaminase associated SNVs analyzed for codon context, strand bias, and transitions/transversions. TCGA tumor-normal mutation data was obtained for 10,437 patients, representing 31 of the most prevalent forms of cancer. Stratified random sampling was used to split patients into training, tuning and validation cohorts for each cancer type. Cancer specific machine learning (XGBoost) models were built using the output from the P142 panel to predict patient Progression Free Survival (PFS) status as either “High PFS” or “Low PFS”. Predictive performance of each model was evaluated using the validation cohort. Models accurately predicted PFS status for several cancer types, including adrenocortical carcinoma, glioma, mesothelioma, and sarcoma. In conclusion, the P142 panel of metrics successfully predicted cancer progression status in patients with some, but not all cancer types analyzed. These results pave the way for future studies on cancer progression associated signatures.

Liquid Biomarkers for Pediatric Brain Tumors: Biological Features, Advantages and Perspectives

Tumors of the central nervous system are the most frequent solid tumor type and the major cause for cancer-related mortality in children and adolescents. These tumors are biologically highly heterogeneous and comprise various different entities. Molecular diagnostics are already well-established for pediatric brain tumors and have facilitated a more accurate patient stratification. The availability of targeted, biomarker-driven therapies has increased the necessity of longitudinal monitoring of molecular alterations within tumors for precision medicine-guided therapy. Nevertheless, diagnosis is still primarily based on analyses of the primary tumor and follow-up is usually performed by imaging techniques which lack important information on tumor biology possibly changing the course of the disease. To overcome this shortage of longitudinal information, liquid biopsy has emerged as a promising diagnostic tool representing a less-invasive source of biomarkers for tumor monitoring and therapeutic decision making. Novel ultrasensitive methods for detection of allele variants, genetic alterations with low abundance, have been developed and are promising tools for establishing and integrating liquid biopsy techniques into clinical routine. Pediatric brain tumors harbor multiple molecular alterations with the potential to be used as liquid biomarkers. Consequently, studies have already investigated different types of biomarker in diverse entities of pediatric brain tumors. However, there are still certain pitfalls until liquid biomarkers can be unleashed and implemented into routine clinical care. Within this review, we summarize current knowledge on liquid biopsy markers and technologies in pediatric brain tumors, their advantages and drawbacks, as well as future potential biomarkers and perspectives with respect to clinical implementation in patient care.

Clinical, Genomic, and Pharmacological Study of MYCN-Amplified RB1 Wild-Type Metastatic Retinoblastoma

An uncommon subgroup of unilateral retinoblastomas with highly aggressive histological features, lacking aberrations in RB1 gene with high-level amplification of MYCN (MCYNamplRB1+/+) has only been described as intra-ocular cases treated with initial enucleation. Here, we present a comprehensive clinical, genomic, and pharmacological analysis of two cases of MCYNamplRB1+/+ with orbital and cervical lymph node involvement, but no central nervous system spread, rapidly progressing to fatal disease due to chemoresistance. Both patients showed in common MYCN high amplification and chromosome 16q and 17p loss. A somatic mutation in TP53, in homozygosis by LOH, and high chromosomal instability leading to aneuploidy was identified in the primary ocular tumor and sites of dissemination of one patient. High-throughput pharmacological screening was performed in a primary cell line derived from the lymph node dissemination of one case. This cell line showed resistance to broad spectrum chemotherapy consistent with the patient's poor response but sensitivity to the synergistic effects of panobinostat-bortezomib and carboplatin-panobinostat associations. From these cells we established a cell line derived xenograft model that closely recapitulated the tumor dissemination pattern of the patient and served to evaluate whether triple chemotherapy significantly prolonged survival of the animals. We report novel genomic alterations in two cases of metastatic MCYNamplRB1+/+ that may be associated with chemotherapy resistance and in vitro/in vivo models that serve as basis for tailoring therapy in these cases.