Variations in Ewing sarcoma and rhabdomyosarcoma patient outcomes based on treatment center volume.

e18530 Background: Due to their rarity and requirement for multi-modality care, evidence suggests (and guidelines recommend) patients (pts) with Ewing Sarcoma (ES) and rhabdomyosarcoma (RMS) treated at high volume centres (HVC) with multidisciplinary tumour board discussions (MTDs) have improved outcomes. However, access to care at HVC is challenging for pts who live remotely, such as many pts in British Columbia (BC), Canada. Our study explores the difference in outcomes of patients with ES and RMS based on location of diagnosis and treatment in BC. Methods: A multi-center retrospective chart review of adults diagnosed with ES and RMS Jan 1st 2000 to Dec 31st 2020 was performed for pts undergoing curative intent therapy at one of six provincial cancer centers. All pts underwent expert pathology review. Descriptive statistics were performed. Fisher’s exact and chi-squared tests were used to evaluate associations. Cox proportional hazards model was used to assess for predictors of better survival outcomes by treatment centre. HVCs was defined as those that saw ≥15 patients. Results: 77 patients were included in this analysis; 46 (60%) and 31 (40%) were treated at HVC and LVC respectively. By HVC and LVC respectively, mean age was 36 and 35, 14 (45%) and 20 (43%) were female, 23 (74%) and 26 (57%) had ES, and 11 (35%) and nine (20%) had localized disease. Pts treated at HVCs were more likely to: receive curative intent radiation (p = 0.006), be presented at MTDs (p = 0.042), and less likely to experience disease progression on fist line therapy (p = 0.04) (Table). Time from biopsy to start of chemotherapy (chemo) was 13 days sooner at HVCs vs LVCs (34 vs 47 days, p = 0.12). Initial chemo regimen (p = 0.25) and surgical treatment (p = 0.75) were not significantly different between HVCs vs LVCs. Age, ECOG, stage, and Charlson Comorbidities Index (CCI) were all significant contributors to overall survival (OS). There was no statistically significant difference in OS by treatment center (HR 0.68, 95% CI 0.36 – 1.29). Conclusions: Variations in care exist for both treatment and outcomes amongst ES and RMS pts treated at HVC vs LVC in BC. Pts treated at HVCs were more likely to be presented at MTDs, to receive curative intent radiation, and less likely to experience disease progression. This may reflect differences in access to resources, sarcoma-specific clinician specialists, and familiarity with upfront aggressive treatment protocols. This study can be used to better inform decisions regarding triaging and centralization of curable ES and RMS patients.[Table: see text]