Abstract BACKGROUND Relapsed central nervous system germinomas are rare with no universal agreement regarding management. We explored the prognostic factors that may impact the treatment of patients with relapsed CNS germinoma. METHODS We collected data on relapsed/progressive germinomas from nine large international sites. Data was summarized using descriptive statistics. Overall survival (OS) was evaluated using Kaplan-Meier and Fischer’s exact test to estimate odds ratios (OR) and 95% confidence intervals (CI). RESULTS Twenty-seven patients with relapsed (24) and progressive (3) germinomas were included (3.7% metastatic). Median age at diagnosis was 15.8 years (interquartile range (IQR): 11.9-18.5). Complete remission (CR) after initial treatment (chemotherapy 63.9% and radiotherapy 88.9%) was achieved in 15 patients (55.6%). The median time from diagnosis to relapse/progression was 20.0 months (range: 10.8-65.1 months) with 55.6% occurring within 24 months. Twenty-five patients (92.6%) underwent chemotherapy, 15 (55.6%) received high-dose chemotherapy with stem cell support (HDCx), and 16 received (59.3%) radiotherapy. At last follow-up, 86.6% of HDCx and 87.5% of radiotherapy recipients were alive. Median time to last follow-up was 41.8 months (IQR: 19.6-132.1). Fifteen children (55.6%) achieved CR after therapy and 21 (77.8%) were alive at last follow-up. Of patients receiving irradiation, 12.5% received whole ventricular irradiation, 81.3% craniospinal irradiation, and 6.3% focal irradiation. Chemotherapy at relapse was associated with improved 5-year OS (OR=1.32 95%CI: 1.06-1.64) Re-irradiation at relapse (OR=2.6, 95%CI: 0.36-19.2) and HDCx at relapse (OR=2.17, 95%CI: 0.30-15.71) did not reach statistically significant difference. CR after initial therapy (OR=1.25, 95%CI: 0.97-1.61) was not associated with improved 5-year OS, CR after relapse therapy was associated with increased 5-year OS (OR=3.50, 95%CI: 1.08-11.24) CONCLUSIONS Relapsed CNS germinomas are salvageable at relapse. This ongoing multi-institutional study will contribute to existing knowledge about relapsed/progressive CNS germinomas and inform prospective clinical trials to improve outcomes for children with relapsed/progressive disease.

GCT-29. MULTI-INSTITUTIONAL ANALYSIS OF PEDIATRIC RELAPSED/REFRACTORY CENTRAL NERVOUS SYSTEM GERMINOMAS