(P 454) TREATMENT PATTERNS AND OUTCOMES IN PEDIATRIC AND ADULT PATIENTS WITH EWING AND UNDIFFERENTIATED ROUND BLUE CELL SARCOMAS IN ALBERTA

Objective: Ewing sarcoma (ES) and undifferentiated round cell sarcomas (URCS) are aggressive tumors of bone and soft tissues affecting adolescents and young adults. Standard treatment consists of systemic treatment in addition to surgery and/or radiation therapy (RT) for locoregional management. Generally, surgery is accepted as the modality of choice whenever feasible without significant morbidity. However, the indications for RT either as definitive locoregional management of ES/URCS or as an adjunct to surgery remains controversial. There are variations in the systemic management of ES/URCS in adult compared to pediatric ES/URCS, though it is unclear if the locoregional treatment (LRT) approach also varies in adult compared to pediatric patients. Our study aimed to investigate the LRT patterns and outcomes for ES and URCS within a publicly funded provincial healthcare system in Canada.

Methods: A retrospective chart review and analysis of pediatric and adult patients with ES or URCS treated in Alberta (with a catchment area of approximately 4.5 million people) from 2008 to 2022 was performed. Patients were selected based on a confirmed diagnosis of ES, peripheral neuroectodermal tumor or URCS reviewed by experienced sarcoma pathologists. Desmoplastic round cell tumors were excluded. Patient demographics, pathologic characteristics (including molecular pathology results if available), disease stage at diagnosis, and treatment strategies (including type, timing, and intent of locoregional therapy) were collected in our Integrated Sarcoma Research Program (iSARP) REDCap database. Descriptive statistics were utilized to assess demographics and treatment trends over time. Kaplan-Meier survival and Wilcoxon rank-sum analysis were used to compare clinical outcomes between adult and pediatric patients for event-free survival (EFS) and overall survival (OS), and between patients receiving different LRT.

Results: Eighty patients were treated between 2008 and 2022 with ES or URSC including 67 patients with ES, three patients with CIC-rearranged sarcoma, and 11 patients with non-specified URCS (Table 1). Metastatic disease was present in 36% of all adult patients and in 57% of pediatric patients. EFS in patients with metastatic disease was 8.8 months for adults versus 19.6 months for pediatric patients (p = 0.02). OS for patients with metastatic disease was 11.5 months for adults and 34.5 months for pediatric patients (p = 0.021). In patients with localized disease, median EFS for adults was 33.0 months, while median EFS for pediatric patients was not reached (p = 0.221). Median OS for adults with localized disease was 99.1 months, while median OS for pediatric patients was not reached (p = 0.518, Figure 1). Combination LRT for localized disease was utilized in 34% of adults compared to only 20% of pediatric patients. All patients with localized disease at diagnosis received LRT, but only 67% of patients with metastatic disease received any form of LRT. A numerically larger proportion of adults with metastatic disease received no LRT (56%) compared to children (15%) (Table 2). Concomitant chemotherapy with radiation was provided to 43% of adults receiving RT in the upfront setting compared to 95% of children. Median EFS for all patients (regardless of stage at diagnosis) treated with surgery alone was not reached, versus 76.2 months for patients treated with combined modality LRT and 22.0 months for patients treated with radiation alone. Patients receiving no LRT (3 children and 9 adults) had a median EFS of 6.6 months.

Conclusion: In our cohort, combined modality LRT was used more frequently in adults with localized disease. In addition, adults with metastatic disease were less likely than children to receive any form of LRT in metastatic setting. Despite fewer adults having metastatic disease at initial diagnosis, outcomes for adults were poorer than for pediatric patients. It is unclear whether differences in LRT used in adults compared to pediatric patients contribute to poorer outcomes in adults. More studies are needed to assess the differential efficacy of LRT in adult and pediatric patients with ES and URCS in both localized and metastatic settings. We are planning to expand our analysis through a collaborative national study combining the datasets from several academic sarcoma centers in Canada.