Pediatric tumors share few recurrent mutations and are instead characterized by copy number alterations (CNAs). The cell-free DNA (cfDNA) is a prominent source for the detection of cancer-specific biomarkers in plasma. We profiled CNAs in the tumor tissues for further evaluation of alterations in 1q, MYCN and 17p in the circulating tumor DNA (ctDNA) in the peripheral blood at diagnosis and follow-up using digital PCR. We report that among the different kinds of tumors (neuroblastoma, Wilms tumor, Ewing sarcoma, rhabdomyosarcoma, leiomyosarcoma, osteosarcoma and benign teratoma), neuroblastoma presented the greatest amount of cfDNA, in correlation with tumor volume. Considering all tumors, cfDNA levels correlated with tumor stage, metastasis at diagnosis and metastasis developed during therapy. In the tumor tissue, at least one CNA (at CRABP2, TP53, surrogate markers for 1q and 17p, respectively, and MYCN) was observed in 89% of patients. At diagnosis, CNAs levels were concordant between tumor and ctDNA in 56% of the cases, and for the remaining 44%, 91.4% of the CNAs were present only in cfDNA and 8.6% only in the tumor. Within the cfDNA, we observed that 46% and 23% of the patients had MYCN and 1q gain, respectively. The use of specific CNAs as targets for liquid biopsy in pediatric patients with cancer can improve diagnosis and should be considered for monitoring of the disease response.

Background: Central nervous system (CNS) tumors are the second most frequent type of neoplasm in childhood and adolescence, after leukemia. Despite the incorporation of molecular classification and improvement of protocols combining chemotherapy, surgery, and radiotherapy, CNS tumors are still the most lethal neoplasm in this age group. Mass spectrometry imaging (MSI) is a powerful tool to map the distribution of molecular species in tissue sections. Among MSI techniques, desorption electrospray ionization (DESI-MSI) has been demonstrated to enable reliable agreement with the pathological evaluation of different adult cancer types, along with an acceptable time scale for intraoperative use. Methods: In the present work, we aimed to investigate the chemical profile obtained by DESI-MSI as an intraoperative surgical management tool by profiling 162 pediatric brain biopsies and reporting the results according to the histopathology and molecular profile of the tumors. Results: The 2D chemical images obtained by DESI-MSI allowed us to distinguish tumor-transformed tissue from non-tumor tissue with an accuracy of 96.8% in the training set and 94.3% in the validation set after statistical modeling of our data using Lasso. In addition, high-grade and low-grade tumors also displayed a distinct chemical profile when analyzed by DESI-MSI. We also provided evidence that the chemical profile of brain tumors obtained by DESI-MSI correlates with methylation-based molecular classes and specific immunophenotypes found in brain biopsies. Conclusions: The results presented herein support the incorporation of DESI-MSI analysis as an intraoperative assistive tool in prospective clinical trials for pediatric brain tumors management in the near future.

Developing advanced preclinical models and targeted therapies is essential for reducing cancer-related deaths in children with solid tumors. Patient-derived xenografts (PDX) have the potential to replicate key elements of the original tumor, including morphology, genetic alterations, and microenvironment, making them valuable tools for studying tumor biology and drug response. We implanted 124 pediatric solid tumor samples, collected for 1 y, into NOD/SCID/IL2Rg (NSG) mice. Tumor fragments were placed subcutaneously, and the animals were monitored for up to 1 y. Histopathology, Short Tandem Repeat (STR) profiling, RT-PCR and/or RNA-sequencing were performed to confirm tumor identity and detect driver fusions. Fifty-five xenografts were successfully established (44.35% of implanted samples), representing 19 tumor types. Sarcomas, notably osteosarcoma, Ewing sarcoma, synovial sarcoma, and rhabdomyosarcoma, displayed first-generation engraftment rates above 55%. Central nervous system tumors had lower success, reflecting unique microenvironmental requirements. Histopathology and STR concordances were 85.45% and 81.1%, respectively, while 92.6% of sarcoma PDXs retained original fusion genes. Second-generation xenografts showed faster growth, suggesting adaptation to the murine host. Sporadic discrepancies, such as new fusions or lymphoproliferative expansions, indicated the need for ongoing molecular validation parallel to other techniques. A pediatric PDX biobank can effectively capture key tumor features while facilitating the study of therapeutic responses and tumor evolution. Our models confirm the feasibility of achieving stable histological and molecular profiles, offering a valuable resource for precision oncology research. Ultimately, these pediatric PDXs could accelerate the discovery of targeted therapy and significantly improve treatment outcomes.

Embryonic tumors share few recurrent mutations, suggesting that other mechanisms, such as aberrant DNA methylation, play a prominent role in their development. The loss of imprinting (LOI) at the chromosome region 11p15 is the germline alteration behind Beckwith–Wiedemann syndrome that results in an increased risk of developing several embryonic tumors. This study analyzed the methylome, using EPIC Beadchip arrays from 99 sporadic embryonic tumors. Among these tumors, 46.5% and 14.6% presented alterations at imprinted control regions (ICRs) 1 and 2, respectively. Based on the methylation levels of ICR1 and ICR2, four clusters formed with distinct methylation patterns, mostly for medulloblastomas (ICR1 loss of methylation (LOM)), Wilms tumors, and hepatoblastomas (ICR1 gain of methylation (GOM), with or without ICR2 LOM). To validate the results, the methylation status of 29 cases was assessed with MS-MLPA, and a high level of agreement was found between both methodologies: 93% for ICR1 and 79% for ICR2. The MS-MLPA results indicate that 15 (51.7%) had ICR1 GOM and 11 (37.9%) had ICR2 LOM. To further validate our findings, the ICR1 methylation status was characterized via digital PCR (dPCR) in cell-free DNA (cfDNA) extracted from peripheral blood. At diagnosis, we detected alterations in the methylation levels of ICR1 in 62% of the cases, with an agreement of 76% between the tumor tissue (MS-MLPA) and cfDNA methods. Among the disagreements, the dPCR was able to detect ICR1 methylation level changes presented at heterogeneous levels in the tumor tissue, which were detected only in the methylome analysis. This study highlights the prevalence of 11p15 methylation status in sporadic embryonic tumors, with differences relating to methylation levels (gain or loss), location (ICR1 or ICR2), and tumor types (medulloblastomas, Wilms tumors, and hepatoblastomas).

Paediatric central nervous system (CNS) tumours are the second most common childhood malignancy and the leading cause of cancer‐related mortality in this age group. Histopathological diagnosis can be challenging, particularly for rare or ambiguous tumours, and may result in misclassification. To evaluate the utility of DNA methylation profiling in a middle‐income country, we performed the Infinium MethylationEPIC BeadChip (Illumina) on tumours from 182 paediatric patients treated at a reference centre for paediatric oncology in Campinas, state of São Paulo, Brazil. Data were analysed using the DKFZ/Heidelberg CNS tumour classifier (v12.8). After excluding control tissue, 163 samples (89.6%) were suitable for classification; 135 (74.2%) achieved a calibrated score ≥ 0.9 and were assigned to a methylation class family. Methylation profiling resulted in a tumour subtype for 88 cases (65.7%) and changed the diagnosis in 28 cases (20.9%), identifying several rare tumour subtypes that were identified solely through methylation analysis, confirming the value of this method in improving diagnostic accuracy. This study highlights the utility of DNA methylation profiling for paediatric CNS tumours in a resource‐limited setting and provides a cohort from an underrepresented middle‐income population to international molecular databases.

Childhood cancer survivors often experience late adverse effects that may be linked to chemotherapy mutagenesis. We studied chemotherapy mutagenesis in normal pediatric tissues using duplex sequencing (NanoSeq) to enable the detection of mutations from single DNA molecules. We found that platinum chemotherapeutics increased the mutation burdens of normal pediatric tissues to levels seen in adults. In the liver, platinum agents imparted a tissue-specific mutational signature that was absent from other tissues. Gene-focused duplex sequencing revealed that chemotherapy mutagenesis generates a great diversity of nonsynonymous variants, some of which may have functional potential, such as leukemogenic variants in blood. Our findings demonstrate extensive chemotherapy mutagenesis in normal tissues of children, which may provide a plausible link between chemotherapy exposure and adverse effects in later life.