ETMR-23. CNS SARCOMAS WITHCIC- ORATXN1-ALTERATIONS — A META-ANALYSIS OF CLINICAL AND MOLECULAR FEATURES IN A LARGE SERIES OF PATIENTS

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Abstract BACKGROUND In 2021, the 5th WHO classification of central nervous system (CNS) tumors acknowledged CNS sarcomas with CIC alterations as a distinct tumor type, which may also expand to non-CIC alterations including ATXN1. To tackle the lack of treatment protocols for these highly aggressive tumors, we conducted a meta-analysis to provide an overview of clinical and molecular characteristics, define clinically relevant subtypes, and ultimately advise on treatment guidelines. METHODS We collected molecular and clinical data for >200 patients with CIC- or ATXN1-altered CNS sarcomas by screening our in-house DNA methylation database (581 potential patients initially identified), publication databases (50 patients), and contacting centers worldwide (60 patients). Tumor tissue (FFPE and fresh frozen) for further molecular characterization was obtained from a subset of patients. DNA methylation-based clustering analyses (t-SNE, UMAP, consensus partitioning) were performed, integrating gene fusion details (RNAseq, FISH), copy-number variations, and clinical patient data to identify associations between (epi-)genetic and clinical parameters. RESULTS Most prominent fusion partners for CIC (n=47) and ATXN1 (n=9) were NUTM1 (n=18), LEUTX (n=17) and DUX4 (n=15). Clustering analyses of DNA methylation patterns indicated several epigenetic subtypes associated with different fusion types. Potential clinical implications are still under evaluation. Age distribution of patients at diagnosis in this cohort ranged from two months to 71 years (median=7.5 years). We observed no gender bias. Survival analyses are currently being performed, first results on survival and follow-up studies will be shown at the symposium. CONCLUSION We show first-of-its-kind data describing a large cohort of CNS sarcomas with CIC or ATXN1 alterations, outlining molecular and clinical characteristics, which may facilitate the development of guidelines for optimal treatment of these tumors based on retrospective response data. New molecular insights may also open up an avenue for targeted therapeutic approaches.