Abstract BACKGROUND Ependymomas are neuroepithelial tumours that can be classified into distinct molecular subgroups, each exhibiting a unique clinical outcome. Therapeutic efforts against the most aggressive and abundant subgroup of pediatric ependymoma (posterior fossa group A, PFA) have traditionally been hampered by a lack of known recurrent driver mutations. However, approximately 25% of PFA tumours exhibit gains of the chromosome arm 1q which is associated with an extremely poor prognosis despite aggressive treatment. By interrogating the multi-omic landscape of PFAs harbouring this copy number variation, we aimed to uncover genetic dependencies from which actionable therapeutics could be derived. METHODS Transcriptomic (bulk/single-cell RNA sequencing), proteomic (LC-MS/MS) and phosphoproteomic analyses were conducted on patient tissues and primary patient-derived cell lines to gain insight into the pathways that drive 1q gain pathogenesis. Chromatin immunoprecipitation sequencing of H3K27me3 and H3K27ac marked histones was carried out to profile the epigenetic landscape of these tumours, and whole genome CRISPR knockout screens were performed to reveal the contribution of essential genes unique to tumours harboring 1q gains. RESULTS Through the comparison of 1q gain and balanced PFA samples, our multi-omic analyses identified the up-regulation and essentiality of known glioma oncogenic drivers previously uncharacterized in PFA. The investigation of essential candidate genes showed a convergence on pathways related to ciliogenesis, with genetic vulnerabilities informing in vitro drug screening. Candidate genes were further validated by in vivo knockdown using established xenograft mouse models for pre-clinical testing. CONCLUSIONS This combined approach has allowed for the derivation of a functional cancer signature underlying 1q gains in PFA and presents novel therapeutic targets for this high-risk subgroup. PFA ependymoma is a deadly malignancy whose complex biology has so far eluded therapy, and new insights from this project will help to identify the first effective therapies for this vulnerable patient population.