Genomic studies of pediatric cancer have primarily focused on specific tumor types or high-risk disease. Here, we used a three-platform sequencing approach, including whole genome (WGS), exome, and RNA sequencing, to examine tumor and germline genomes from 309 prospectively identified children with newly diagnosed (85%) or relapsed/refractory (15%) cancers, unselected for tumor type. Eighty-six percent of patients harbored diagnostic (53%), prognostic (57%), therapeutically-relevant (25%), and/or cancer predisposing (18%) variants. Inclusion of WGS enabled detection of activating gene fusions and enhancer hijacks (36% and 8% of tumors, respectively), small intragenic deletions (15% of tumors) and mutational signatures revealing of pathogenic variant effects. Evaluation of paired tumor-normal data revealed relevance to tumor development for 55% of pathogenic germline variants. This study demonstrates the power of a three-platform approach that incorporates WGS to interrogate and interpret the full range of genomic variants across newly diagnosed as well as relapsed/refractory pediatric cancers. STATEMENT OF SIGNIFICANCEPediatric cancers are driven by diverse genomic lesions and sequencing has proven useful in evaluating high risk and relapsed/refractory cases. We show that combined whole genome, exome, and RNA-sequencing of tumor and paired normal tissues enables identification and characterization of genetic drivers across the full spectrum of pediatric cancers.Research.

Cancer genomics has illuminated a wide spectrum of genes and core molecular processes contributing to human malignancy. Still, the genetic and molecular basis of many cancers remains only partially explained. Genetic predisposition accounts for 5-10% of cancer diagnoses 1,2 and genetic events cooperating with known somatic driver events are poorly understood. Analyzing established cancer predisposition genes in medulloblastoma (MB), a malignant childhood brain tumor, we recently identified pathogenic germline variants that account for 5% of all MB patients 3 . Here, by extending our previous analysis to include all protein-coding genes, we discovered and replicated rare germline loss-of-function (LoF) variants across Elongator Complex Protein 1 (ELP1) on 9q31.3 in 15% of pediatric MB SHH cases, thus implicating ELP1 as the most common MB predisposition gene and increasing genetic predisposition to 40% for pediatric MB SHH . Inheritance was verified based on parent-offspring and pedigree analysis, which identified two families with a history of pediatric MB. ELP1-associated MBs were restricted to the molecular SHHα subtype 4 and were characterized by universal biallelic inactivation of ELP1 due

Cancer risk is highly variable in carriers of the common TP53-R337H founder allele, possibly due to the influence of modifier genes. Whole-genome sequencing identified a variant in the tumor suppressor XAF1 (E134*/Glu134Ter/rs146752602) in a subset of R337H carriers. Haplotype-defining variants were verified in 203 patients with cancer, 582 relatives, and 42,438 newborns. The compound mutant haplotype was enriched in patients with cancer, conferring risk for sarcoma (P = 0.003) and subsequent malignancies (P = 0.006). Functional analyses demonstrated that wild-type XAF1 enhances transactivation of wild-type and hypomorphic TP53 variants, whereas XAF1-E134* is markedly attenuated in this activity. We propose that cosegregation of XAF1-E134* and TP53-R337H mutations leads to a more aggressive cancer phenotype than TP53-R337H alone, with implications for genetic counseling and clinical management of hypomorphic TP53 mutant carriers.

Background Patients with cancer are increasingly offered genomic sequencing, including germline testing for cancer predisposition or other disorders. Such testing is unfamiliar to patients and families, and clear communication is needed to introduce genomic concepts and convey risk and benefit information. Methods Parents of children with cancer were offered the opportunity to have their children’s tumor and germline examined with clinical genomic sequencing. Families were introduced to the study with a 2‐visit informed consent model. Baseline genetic knowledge and self‐reported literacy/numeracy were collected before a study introduction visit, during which basic concepts related to genomic sequencing were discussed. Information was reinforced during a second visit, during which informed consent was obtained and a posttest was administered. Results As reflected by the percentage of correct answers on the pretest and posttest assessments, this model increased genetic knowledge by 11.1% (from 77.8% to 88.9%; P < .0001) in 121 parents participating in both the study introduction and consent visits. The percentage of parents correctly identifying the meaning of somatic and germline mutations increased significantly (from 18% to 59% [somatic] and from 31% to 64% [germline]; P < .0001). Nevertheless, these concepts remained unfamiliar to one‐third of the parents. No relation was identified between the change in the overall percentage of correct answers and self‐reported literacy, numeracy, or demographics. Conclusions The use of a 2‐visit communication model improved knowledge of concepts relevant to genomic sequencing, particularly differences between somatic and germline testing; however, these areas remained confusing to many participants, and reinforcement may be necessary to achieve complete understanding.

The advent of next-generation sequencing (NGS) has introduced an exciting new era in biomedical research. NGS forms the foundation of current genetic testing approaches, including targeted gene panel testing, as well as more comprehensive whole-exome and whole-genome sequencing. Together, these approaches promise to provide critical insights into the understanding of health and disease. However, with NGS testing come many ethical questions and concerns, particularly when testing involves children. These concerns are especially relevant for children with cancer, where the testing of tumor and germline tissues is increasingly being incorporated into clinical care. Areas covered: In this manuscript, we explore the key ethical considerations related to conducting germline NGS testing in pediatric oncology, focusing on the four main principles of beneficence, non-maleficence, autonomy and justice. Expert commentary: The ethical issues surrounding germline NGS testing are complex and result in part from our limited understanding of the medical relevance of many of the results obtained and poor knowledge of the impacts of testing, both beneficial and detrimental, on patients and their families. In this article we discuss the risks and benefits of germline NGS testing and the arguments for and against such testing in children with cancer.