Outcomes following radiation therapy for embryonal tumor with multilayered rosettes (ETMR): results from the Pediatric Proton/Photon Consortium Registry (PPCR).

Purpose: Embryonal tumor with multilayered rosettes (ETMR) is a rare pediatric CNS embryonal tumor with poor survival. The Pediatric Proton/Photon Consortium Registry (PPCR) was queried for outcomes data from prospectively consenting pediatric patients with ETMR treated with proton radiation therapy (RT).

Methods: 20 patients (2013-2021) at 9 institutions had ETMR; 2 with prior RT were excluded from statistical analyses (PPCR ETMR, N = 18). Overall Survival (OS) and Event Free Survival (EFS) analyses were performed using the Kaplan-Meier method and log-rank values. Median follow-up was calculated using the reverse Kaplan-Meier method.

Results: Median age at RT was 3.0 years (1.7-12.2); median follow-up was 55.5 months (2.6-119.4). 8 patients (44%) expired and 6 patients (33%) are surviving ≥ 55 months. 11 (61%) patients received systemic therapy with stem cell support. The majority (89%) had focal RT (median dose 54 Gy), while 2 patients received craniospinal irradiation (CSI, 30.6-36 Gy). 4-year OS and EFS were 59.6% and 54.2%, respectively. Local control (LC) at 4 years was 81%. No differences in OS or EFS were observed for receipt of systemic therapy with stem cell support (p = 0.361, p = 0.57), progression prior to RT (p = 0.127, p = 0.18), or surgery to RT ≥ 200 days (p = 0.35, p = 0.254). Symptomatic radionecrosis was not reported.

Conclusion: Focal proton RT provided effective local control as part of multimodality therapy for ETMR, with encouraging survival for this rare and often infant age tumor. Outcomes for CSI were limited to 2 patients treated upfront, and 1 patient receiving salvage CSI for disseminated relapse after focal RT who is surviving > 1 year.

Trial registration: DFCI protocol 12-103, clinicaltrials.gov NCT01696721, date of registration 9/27/2012.