ID #595 Salvage Re-irradiation Strategies in Relapsed Pediatric Ependymoma: Insights from Two Leading Pediatric Oncology Centers in Brazil and Argentina

Background The prognosis for recurrent pediatric ependymoma remains guarded, and consensus regarding the optimal re-irradiation (RT2) field volume is currently lacking. This study evaluates clinical outcomes in a pediatric cohort undergoing RT2, specifically comparing the efficacy of craniospinal irradiation (CSI) versus focal radiotherapy. Methods A multi-institutional retrospective analysis was conducted on 44 pediatric patients treated between 2005 and 2025 at two tertiary centers in Brazil and Argentina. All subjects had previously received focal radiotherapy (RT1) as part of their initial treatment. Results The cohort (median age: 2.96 years) was characterized by a predominance of infratentorial (90.9%) and histological grade 3 (75%) tumors, with molecular profiles identifying 21 PFA and four ZFTA-fused cases. At first relapse, 66.9% of patients presented with isolated local recurrence. Following salvage re-irradiation (RT2), the median overall survival (OS) was 2.54 years. Comparative analysis between craniospinal irradiation (CSI; n = 23; median 36 Gy) and focal radiotherapy (focal-RT2; n = 20; median 50.4 Gy) revealed no statistically significant differences in 3-year progression-free survival (40.2% vs.32.5%; p = 0.751) or 3-year OS (47.7% vs. 34.6%; p = 0.566). Furthermore, CSI demonstrated no therapeutic superiority over focal-RT2 in the subgroup of patients with isolated local relapse (p = 0.927). Conclusions Re-irradiation serves as a feasible salvage strategy for recurrent ependymoma; however, the lack of significant survival benefit for CSI over focal-RT2, particularly in cases of isolated local failure, indicates that the optimal target volume remains equivocal. These findings underscore the necessity for prospective trials to validate focal irradiation as a standard for localized recurrence, potentially averting the cumulative morbidity associated with craniospinal fields. 1. Tsang DS, Burghen E, Klimo P Jr, Boop FA, Ellison DW, Merchant TE. Outcomes After Reirradiation for Recurrent Pediatric Intracranial Ependymoma. Int J Radiat Oncol Biol Phys. 2018;100(2):507-515. doi:10.1016/j.ijrobp.2017.10.002