SIOP Ependymoma I: Final results, long term follow-up and molecular analysis of the trial cohort: A BIOMECA Consortium Study

Background: SIOP Ependymoma I was a non-randomised trial assessing event free and overall survival (EFS/OS) from non-metastatic intracranial ependymoma in children aged 3 to 21 years, treated with a staged management strategy. Chemotherapy efficacy in ependymoma is debated and therefore the response rate (RR) of subtotally resected (STR) ependymoma to vincristine, etoposide and cyclophosphamide (VEC) was an additional primary outcome. We report final results with 12-year follow-up and post hoc analyses of recently described biomarkers. Methods: 74 participants were eligible. Children with gross total resection (GTR) received radiotherapy, whilst those with STR received VEC before radiotherapy. DNA methylation and 1q status were evaluated, alongside hTERT, ReLA, Tenascin-C, H3K27me3 and pAKT expression. Results: Five- and ten-year EFS was 49.5% and 46.7%, OS was 69.3% and 60.5%. GTR was achieved in 33/74 (44.6%) and associated with improved EFS (p=0.003, HR=2.6, 95% confidence interval (CI) 1.4-5.1). Grade 3 tumours were associated with worse OS (p=0.005, HR=2.8, 95%CI 1.3-5.8). 1q gain and hTERT expression were associated with poorer EFS (p=0.003, HR=2.70, 95%CI 1.49-6.10 and p=0.014, HR=5.8, 95%CI 1.2-28 respectively) and H3K27me3 loss with worse OS (p=0.003, HR=4.6, 95%CI 1.5-13.2). DNA methylation profiles showed expected patterns. 12 participants with STR did not receive chemotherapy; a protocol violation. However, chemotherapy RR was 65.5% (19/29, 95%CI 45.7-82.1), exceeding a prespecified 45% RR. Conclusions: RR of STR to VEC exceeded the pre-specified criterion for efficacy. However, cases of inaccurate treatment stratification highlighted the need for rapid central review. Prognostic associations for 1q gain, H3K27me3 and hTERT were confirmed.