Abstract 4337: Illuminating the complex rearrangement landscape of sarcoma

Abstract Structural rearrangements and in particular, gene fusions, are key mutational processes in bone and soft tissue tumors, used for both disease classification and as biomarkers. However, the mutational processes and rearrangement processes underlying many of these events remain poorly characterized. Recent data indicate that sarcomas show particularly high frequencies of complex rearrangement events, including patterns which do not fit those of known mutational mechanisms. As the largest whole genome sequencing (WGS) cohort of sarcomas to date, the Genomics England (GE) 100,000 Genomes project represents a unique dataset in which to profile these events. Structural variants (SVs) were identified in whole genome sequencing data for 978 samples from the Genomics England 100,000 Genomes Project using an optimized approach based on 5 specialized SV callers. SVs identified by at least 2 callers were filtered to retain only those which passed the quality filter, and to remove variants present in either matched germline samples or >1% of a panel of normal variants. Chromothriptic events, extrachromosomal DNA (ecDNA) and genes enriched for SVs were identified using established algorithms. The prevalence of SVs varies across sarcoma, in keeping with previous reports, with particularly high rates observed in myxofibrosarcoma and liposarcoma. As described previously, liposarcomas showed the highest rates of chromothripsis. We have examined some tumor types at higher granularity than previously available, demonstrating directly that the rates of complex rearrangement events vary across subtypes. For example, chromothriptic events are identified in 100% of well-differentiated liposarcomas, but less than 10% of myxoid liposarcomas. Similarly, the presence of ecDNA varies by tumor type, with the novel observation of particularly high rates in angiosarcoma. Using these data, we have catalogued the rearrangement patterns generating canonical gene fusions in fusion-driven soft tissue tumor types. Despite more recent advances in histological classification, survival for patients with sarcoma has remained largely unchanged for 40 years. Characterization of the mutational processes underlying these rearrangements will shed light on the pathogenesis of these tumors. Citation Format: Sara Waise, Tom Lesluyes, Jonas Demeulemeester, Maxime Tarabichi, Adrienne Flanagan, Nischalan Pillay, Peter Van Loo. Illuminating the complex rearrangement landscape of sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4337.