Molecular Epidemiology of Pediatric Germ Cell Tumors

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DESCRIPTION (provided by applicant): Pediatric germ cell tumors (GCTs) are a heterogeneous group of tumors that are hypothesized to occur as a result of events in utero, which suggests that alterations in processes required for normal embryonic development are likely to be especially relevant to etiology. The incidence of pediatric GCTs has increased in recent years in certain subgroups, and the underlying causes are unknown. Given the early age of onset, genetic contributions seem likely. Aberrant DNA methylation, which has been implicated in the etiology of multiple types of cancer, has the potential to be especially relevant in GCTs due to the extensive epigenetic reprogramming that occurs in the germ line and early embryo during normal development. The primary objective for this proposal is to conduct a comprehensive case-parent triad study of genetic and epigenetic alterations in pediatric GCTs using the resources of the Children's Oncology Group (COG) and the Childhood Cancer Research Network (CCRN) in the United States and Canada. Cases of pediatric GCT (ages 0-19 years) diagnosed from July 1, 2008-December 31, 2015 will be identified through the CCRN and will be invited to participate. We expect to enroll approximately 930 cases. DNA samples will be collected from the cases and their parents for use in genetic analyses, tumor specimens will be obtained for evaluation of epigenetic alterations, and lifestyle and environmental risk factors will be assessed using mailed questionnaires. We hypothesize that genetic variation in key pathways relevant to germ cell development will be associated with pediatric GCT. We further hypothesize that because the histologic subtype of the tumor is dependent on the degree of differentiation that has occurred at the time of transformation, DNA methylation patterns will differ by tumor histology. Our primary aims will be to: 1) Evaluate associations between genetic variation (including deep sequencing of selected genes) in key pathways involved in germ cell development and pediatric GCT using a case-parent triad design and 2) Explore heterogeneity in DNA methylation by tumor histology. We will genotype single nucleotide polymorphisms (SNPs) from relevant biological pathways using the Illumina platform. Candidate SNPs will be selected using a tagSNP approach supplemented with SNPs that have been previously reported to have functional significance. In addition, deep re-sequencing will be used to identify variants in four genes that are associated with pediatric GCTs in our pilot data, KITLG, SPRY4, BAK1, and DMRT1. We will evaluate genome wide DNA methylation using the Illumina HumanMethylation27 BeadChip, which will allow us to select CpG sites that are characteristic of GCTs. The research proposed in this application is significant because it will be the largest genetic epidemiology study of pediatric GCTs to date and it will evaluate novel associations with respect to genetic susceptibility. In addition, understanding methylation patterns in pediatric GCTs may indicate the developmental stage at which the tumor arose. PUBLIC HEALTH RELEVANCE: Pediatric germ cell tumors (GCTs) are cancers that affect approximately 360 children per year; the incidence rates for some pediatric GCTs are rising. Little is known about why these types of cancers develop in children, but it is possible that abnormalities in underlying genetic processes that occur during fetal development play a role. We are proposing the largest molecular epidemiology study ever conducted to evaluate the contribution of underlying genetic susceptibility to the development of pediatric GCT. Our goal is to provide important insights on how early-life events may lead to long-term alterations in gene function and increase the risk of cancer.