The Molecular Landscape of ETMR at Diagnosis and Relapse [gene expression]

ETMRs are aggressive pediatric embryonal brain tumors with universally dismal outcome. We collected 193 ETMR samples and an additional 23 matched relapses to investigate the genomic landscape of this distinct entity. We found that patients having tumors without C19MC amplification, the proposed driver, frequently harbor DICER1 germline mutations or other miRNA-related aberrations such as somatic miR-17-92 miRNA cluster amplifications. Despite these distinct genetic aberrations, no molecular subgrouping was observed. Whole-genome sequencing revealed an overall low recurrence of SNVs, but prevalent R-loop-associated chromosomal instability, of which we show that this can be induced by loss of DICER1 function. Comparing primary tumors and matched relapses revealed a strong conservation of SVs but low conservation of SNVs. Moreover, many newly acquired SNVs are associated to a new cisplatin treatment related mutational signature. Finally, we show that targeting R-loops with topoisomerase and PARP inhibitors might be an effective treatment strategy for this deadly disease. RNA was extracted from fresh frozen tumor material of 28 different ETMR patients and profiled on Affymetrix Human Genome U133 Plus 2.0 arrays to study the general gene expression patterns defining ETMRs and to compare this to other entities.