ATRT-09. Outcome and therapeutic interventions in relapsed and refractory ATRT – The EU-RHAB perspective

Abstract Currently an internationally accepted consensus treatment for relapsed/refractory ATRT is missing. Little known about relapse patterns, prognostic factors and outcome. In a recently published cohort of 143 ATRTs from the EU-RHAB registry, progression on therapy or occurred in 64% (n=91). Previously strategies failure have been restricted to individual, mostly clinically guided, attempts early phase trials with limited sample sizes. We present 55 patients identified between 2015 2021 (total recruited n=147). Median age was 19 months; 27.3% (n=15) germline mutation identified. A total 43/55 tumors were subgrouped [60.5% SHH (n=26), 14.0% MYC (n=6), 23.3% TYR (n=10), one patient SHH+TYR]. Salvage applied 83.6% (46/55). Sixty 17 different regimens subclassified into conventional chemotherapy, epigenetic, targeted metronomic 40/55 patients. overall survival (OS) 20±1.8 weeks following first event, median time 11±1.8 weeks. 12 months OS 23.1%. No significant differences noted molecular subgroups; neither SMARCB1 prognostic. Patients <12 (n=9;16.4%) had significantly reduced compared older (9±6.0wks vs. 22±3.2wks, p<0.05) Those who received according approaches such as MEMMAT (8/55;14.5%) survived longer than treated other regimens, including epigenetic therapy. (72±36.8wks 25±6.2wks, Our data provide valuable insights vulnerable group deserving evidence based clinical management access all phases. Prospectively we aim merge results other, international cohorts generate more robust results.