Circular extrachromosomal DNA promotes tumor heterogeneity in high-risk medulloblastomas

Circular extrachromosomal DNA (ecDNA) in patient tumor genomes is an important driver of oncogenic gene expression, evolution of drug resistance, and poor patient outcomes. Applying computational methods for detection and reconstruction of ecDNA across a retrospective cohort of 481 medulloblastoma (MB) tumors from 465 patients, we identify circular ecDNA in 82 patients (18%). Patients with ecDNA+ MB were more than twice as likely to relapse and three times as likely to die within 5 years of diagnosis. Individual tumors harbor multiple ecDNA lineages, each containing distinct amplified oncogenes. Multimodal sequencing, imaging, and CRISPR inhibition experiments in MB models reveal intratumoral heterogeneity of ecDNA copy number per cell and frequent putative "enhancer rewiring" events on ecDNA. This study reveals the frequency and diversity of ecDNA in a subset of highly aggressive MB tumors, and suggests copy number heterogeneity and enhancer rewiring as clinically relevant features of ecDNA in MB.