3045 - Radiotherapy for Adolescents and Young Adults with Ewing Sarcoma and Rhabdomyosarcoma Compared to Children

K. Meijer¹, A. Bel¹, O. Husson^2,3, B. Balgobind¹, and I. W. van Dijk¹; ¹Department of Radiation Oncology, Cancer Center Amsterdam, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands, ²Department of Medical Oncology, Netherlands Cancer Institute-Antoni van Leeuwenhoek, Amsterdam, Netherlands, ³Department of Psychosocial Research and Epidemiology, Netherlands Cancer Institute, Amsterdam, Netherlands

Purpose/Objective(s): The clinical care of adolescent and young adults (AYAs; =18–=39 years) with Ewing sarcoma (ES) and rhabdomyosarcoma (RMS) is challenged by e.g. delayed diagnosis and lower treatment tolerance compared to children (<18 years). Radiotherapy (RT) has a key role in treatment, but literature on RT in AYAs is scarce. We retrospectively compared treatment and outcomes of AYAs with children diagnosed with ES and RMS. Materials/

Methods: From our large AYA and pediatric cohort, we investigated small samples of 8 AYAs and 8 children with ES, and 12 AYAs and children with RMS who received RT between 2000 and 2020 (Table 1). Patient and treatment characteristics, and 5-year survival rates were extracted from medical records. We also compared radiation techniques, dose schemes and acute toxicity.
Results: The median age of AYAs and children was 26.0 (range 18.3–35.0) and 12.2 (range 3.1–17.8) years, respectively. All ES treatments were based on Euro Ewing protocols (1999, 2008), with curative intended RT; total primary tumor doses varying from 42.0–56.0 Gy in AYAs, and 45.0–59.4 Gy in children, all in fractions of 1.8–2.0 Gy. Alveolar RMS was more common in AYAs (8/12) whereas embryonal RMS was more frequent in children (8/12). All RMS patients, regardless of age, were treated according to the EpSSG 2005 RMS protocol, with curative intent in 22/24 patients. Of these, 9 AYAs and 9 children received external beam RT with total doses varying from 41.4–59.4 Gy in fractions of 1.8–2.0 Gy. One AYA and 3 children had 1.25 Gy PDR brachytherapy in the head and neck area; total dose 47.5 Gy in AYAs and 40 Gy in children. Acute toxicity (e.g. fatigue, nausea and diarrhea) was reported for 13/20 AYAs and 14/20 children. Five AYAs and 8 children had radiation-induced dermatitis, and 5 AYAs and 3 children radiation mucositis. In both groups, 5 patients presented with a local recurrence within 5 years after primary treatment. The 5-year relative survival for ES was 38% in both AYAs and children, and for RMS 0% and 83% in AYAs and children, respectively.
Conclusion: In this small sample, radiation doses for RMS in AYAs were lower than in children, but comparable for ES. Acute toxicities were similar, but prognosis and survival rates were worse for AYAs than for children. These findings provide reason to investigate our complete large cohorts.

Abstract 3045 – Table 1: Characteristics of AYAs and children treated for Ewing sarcoma (ES) and rhabdomyosarcoma (RMS) between 2000-2020

	ES; N=16 (%)		RMS; N=24 (%)
	AYAs	Children	AYAs	Children
Gender
Male Female	5 (63) 3 (37)	4 (50) 4 (50)	7 (58) 5 (42)	9 (75) 3 (25)
Metastases
Lymph node Distant	- 3 (37)	- 6 (75)	4 (33) 4 (33)	3 (25) 2 (17)
Treatment
Surgery Chemotherapy	6 (75) 8 (100)	6 (63) 8 (100)	2 (17) 12 (100)	8 (67) 12 (100)
Radiotherapy Head & neck Thorax Abdomen/pelvis Extremities	1 (13) 3 (37) 3 (37) 1 (13)	- 2 (25) 5 (63) 1 (13)	6 (50) 2 (17) 3 (25) 1 (8)	6 (50) - 4 (33) 2 (17)
Note: percentages may not exactly total 100 due to rounding