Prevalence of High Tumor Mutational Burden Among Pediatric Patients With Solid Tumors.

High tumor mutational burden (TMB-H), defined as ≥10 non-driver somatic mutations per mega base of genome sequenced (mut/Mb), and high microsatellite instability (MSI-H), which can lead to TMB-H, are both associated with response to the immunotherapy pembrolizumab. Data from the KEYNOTE-158 study demonstrated that the association between TMB-H and response to pembrolizumab is independent of MSI-H status. Because data in children are limited, the prevalence of TMB-H in pediatric solid tumors is unclear. This study sought to examine TMB-H prevalence across solid tumor types that are most common among pediatric tumors using real-world data. This retrospective, cross-sectional study included data from FoundationCORE® solid tumor biopsies that were sequenced by comprehensive genomic profiling between 2013 and 2023. All patients were <18 years of age at the time of specimen collection. TMB-H prevalence was assessed among patients with non-MSI-H tumors (including those with MSI-low and microsatellite-stable tumors) and by key patient demographics and disease characteristics. Among 3533 patients with non-MSI-H solid tumors, TMB-H prevalence was 1.42% and was significantly higher in children aged 12-17 years than in children aged <12 years (2.17% vs 0.98%; p = 0.006). There were no significant differences based on sex, genomic ancestry, tissue of origin, disease stage at testing, or whether the tissue sample was from a metastatic versus nonmetastatic site. Prevalence varied by tumor type but was <3% across subgroups, including glioma, central nervous system non-glioma, and peripheral nervous system tumors. Overall, TMB-H prevalence was low across solid tumor types that are frequently observed in children.