3527 - Outcomes Following Radiation Therapy (RT) for Embryonal Tumor with Multilayered Rosettes (ETMR): Results from the Pediatric Proton/Photon Consortium Registry (PPCR)

J. M. Krisch¹, R. P. Ermoian², D. J. Indelicato³, J. Y. Lee⁴, J. P. Perentesis⁵, S. M. Perkins⁶, N. N. Laack II⁷, J. Chang⁸, I. MacEwan⁹, S. L. Wolden¹⁰, D. Wang¹, P. D. Aridgides¹, and T. I. Yock¹¹; ¹SUNY Upstate Medical University, Syracuse, NY, ²Department of Radiation Oncology, University of Washington/ Fred Hutchinson Cancer Center, Seattle, WA, ³Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, ⁴Procure Proton Therapy Center, Somerset, NJ, ⁵Cincinnati Children’s Hospital, Cincinnati, OH, ⁶Washington University in St. Louis, St. Louis, MO, ⁷Department of Radiation Oncology, Mayo Clinic, Rochester, MN, ⁸Oklahoma Proton Center, Oklahoma City, OK, ⁹University of California, San Diego, La Jolla, CA, ¹⁰Memorial Sloan Kettering Cancer Center, New York, NY, ¹¹Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA

Purpose/Objective(s): Embryonal tumor with multilayered rosettes (ETMR) represents a rare pediatric CNS embryonal tumor; limited survival estimates are around 25%. Pediatric Proton/Photon Consortium Registry (PPCR) was queried for patient and treatment outcomes data from prospectively consenting pediatric radiotherapy (RT) patients. Materials/

Methods: PPCR ETMR enrolled 20 patients (2013-2021) at 9 institutions; 2 with prior RT at enrollment were excluded from statistical analyses (N=18). Survival (OS, Overall; EFS, Event Free) analyses were performed using Kaplan Meier and log-rank p-values from RT start. Median follow-up was calculated using the reverse Kaplan Meier method.
Results: Median RT age was 3.0 years (range 1.7-12.2) and median follow-up was 55.5 months (2.6-119.4). Patients had surgery, chemotherapy (with or without stem cell support) and proton radiation. Surgery was gross total resection (GTR) or near total resection (NTR) for 89% of patients; two had subtotal resection (STR). All were M0. Ten patients (56%) received high dose chemotherapy. The majority (89%) had focal RT whereas 2 patients received craniospinal (CSI) radiation with boost (30.6Gy or 36Gy). The 2 and 4 year overall survival (OS) were 72.2% and 59.6%, respectively. Local control (LC) was 81% at 2 and 4 years. The 2 year OS for focal RT was 75% and for CSI was 50% (p=0.307). Disseminated CNS relapse-free survival at 2 and 4 years was 74.3%. All relapses occurred within 2 years of RT. Median primary RT dose was 54Gy (range 53-57.6Gy). GTR was not associated with improved OS (2 year OS GTR 66.7%, NTR 75%, STR 100%, p =0.452) or EFS (2 year EFS 50%, NTR 50%, STR 100%, p =0.735). Patients with GTR had similar LC (2 year LC 75%) compared to all others (2 year LC 83.6%, p =0.464). The 2-year OS (p=0.307) and EFS (p=0.621) with high dose chemotherapy were 50% and 50%, compared to 75% and 56.2% without high dose chemotherapy, respectively. Of six patients (32%) with gross disease pre-RT, all had 54Gy focal RT and 5 are alive (4 have no evidence of disease). The median time from surgery to RT start was 186 days. EFS and OS for earlier RT (= 200) compared with delayed RT (>200 days) are shown in the table. There were 6 patients who received focal RT without high dose chemotherapy: 3 are alive without relapse, 2 expired (1 received multiple repeat RT courses), and 1 is surviving 15.2 months after salvage CSI (36Gy plus metastatic site boost) for disseminated only relapse.
Conclusion: Focal proton RT provided effective local control as part of multimodality therapy for ETMR, with encouraging survival for this very rare and often infant age tumor. Outcomes for CSI were limited to 2 patients treated upfront and 1 patient with salvage CSI for disseminated relapse who remains disease free >1 year from reirradiation.

Abstract 3527 – Table 1

Surgery to RT start (days)	EFS 2yr / 4yr (p =0.177)	OS 2yr / 4yr (p=0.243)
= 200 (n=10)	70% / 70%	90% / 67%
> 200 (n=8)	37.5% / 37.5%	50% / 50%