LAUSR

11027 Background: Extra-skeletal ewing sarcomas (ES) are rare, and data on outcomes following standard ES chemotherapy protocols are very limited. Methods: We retrospectively collected data on skeletal and extra-skeletal ES patients who presented with localized disease from January, 2006 to June, 2018. Disease and treatment characteristics were compared between the two groups by the chi-square test. Overall survival (OS) and local recurrence free survival (LRFS) were estimated by the Kaplan-Meier method and compared by the Log-rank test. Results: A total of 120 patients were included. Twenty-nine (24%) had extra-skeletal and 91 (76%) had skeletal ES. Location was in the extremity in 51 (43%) and non-extremity in 69 (57%). For extra-skeletal ES, tumors originated from soft tissue in 23 (79%), and viscera in 6 (21%). All patients received standard vincristine, doxorubicin, and cyclophosphamide alternating with ifosfamide and etoposide (VDC-IE), with a plan for local control at week 12 of the protocol. Local control was by surgery in 76 (63%) and radiotherapy in 44 (37%). At a median follow up of 38 months, there was no difference in 5-year OS between extra-skeletal and skeletal ES patients (67% and 70% respectively, p = 0.96). Patients with visceral ES had inferior 5-year OS compared to all others (soft-tissue extra-skeletal and skeletal ES); 33% vs. 72%; p = 0.013. Resectability rate was not different between extra-skeletal and skeletal ES patients (54% and 69% respectively, p= 0.11). Furthermore, among patients who underwent surgery, there was no difference between extra-skeletal and skeletal ES patients in R0 resection rate (86% and 89% respectively, p= 0.52) and poor ( < 90%) tumor necrosis rate (62% and 46% respectively, p= 0.31). However, more local recurrences (28% vs. 10%, p= 0.034) and inferior 5-year LRFS (74% vs. 83%; p = 0.042) were observed in the extra-skeletal group, although more extra-skeletal patients received adjuvant radiotherapy; 11 (73%) vs. 21 (36%), p = 0.01. Conclusions: Patients with localized extra-skeletal ES have OS outcomes that are comparable to skeletal ES treated with standard VDC-IE chemotherapy. However, extra-skeletal ES patients are at significantly higher risk of local recurrence.