Metagenomic characterization of viruses in the serum of children with newly diagnosed cancer

•What's Known on This Subject•Virus infections, both chronic and transient are common in children. There are several known cancer-causing viruses, and viruses that may complicate cancer treatment in children. There are many studies on individual viruses, but few larger studies.•What This Study Adds•This study provides an overview of the human virome in children diagnosed with different cancer types. It provides data on the prevalence of many viruses. Novel information on HPgV and TTV infections and a new virus were revealed. A large cohort of pediatric patients with various forms of childhood cancer was investigated for the presence of viruses using metagenomics. A total of 476 patient samples, collected between 1989 and 2018, were analyzed, representing various pediatric oncological diagnoses and a control group of non-malignant diagnoses. The study was carried out using metagenomic sequencing of serum samples. Viruses were identified and analyzed using bioinformatics methods, followed by Polymerase chain reaction (PCR) confirmation The results indicate that a wide range of viruses can be detected in the bloodstream of children with newly diagnosed cancer. Nine viral genomes were identified: Human Pegivirus (HPgV), Hepatitis C virus, Parechovirus 1, Rhinovirus C, Human papillomavirus 116, Human polyomavirus 10, Parvovirus B19, and different variants of Torque Teno Virus (TTV). In this study, a previously unknown virus was found belonging to the Iflavirdae family in the order Picornavirales. HPGV was significantly more common in patients with leukemia compared to other conditions. These results highlight the abundance of systemic virus infections in children, and the value of metagenomic sequencing for hypothesis forming regarding the associations between virus infections and cancer.