Evaluation of local control strategies in patients with localized Ewing sarcoma of bone: A report from the Children’s Oncology Group.

Abstract

9537 Background: Patients (pts) with Ewing sarcoma (EWS) require local control, either with surgery alone (S), radiation alone (R), or a combination of surgery + radiation (S+R). Optimal choice of local control for disease control remains unclear. Our primary aim was to determine the mode of local control associated with the highest event-free survival (EFS). Methods: Pts with localized EWS of bone treated on INT0091, INT0154, or AEWS0031 phase III trials were included if they had complete local control data, did not have cranial tumors, received local control starting 2-6 months after enrollment, and were randomized to receive standard dose 5-drug chemotherapy every 3 weeks. We used propensity scores to control for differences in age, tumor site, and year of diagnosis between local control groups. We constructed Cox models controlling for local control propensity scores to assess the impact of local control type on EFS and overall survival (OS) from the start of local control. Results: 465 pts were included. Pts selected for S were treated more recently (p < 0.001), more likely to have appendicular tumors (p < 0.001), and younger (p = 0.02). Pts treated with R, compared to S, had higher unadjusted risk of any event (HR 1.70; 95% CI 1.18 - 2.44; p = 0.004) or death (HR 1.84; 95% CI 1.18 – 2.85; p = 0.006). Pts treated with S+R, compared to S, had higher unadjusted risk of death (HR 1.75; 95% CI 1.10 – 2.76; p = 0.02). After adjusting for propensity scores, there was a trend of higher risk of any event for pts treated with R (HR 1.42; 95% CI 0.94 – 2.14; p = 0.10) compared to S, though this was not statistically significant. No other differences in adjusted risk of event or death between local control groups were statistically significant. We confirmed these results with standard Cox models using age, tumor site, and year of diagnosis as covariates. Conclusions: In this large group of uniformly treated pts, investigator choice of local control approach was not significantly related to EFS. These data support current practice of surgical resection when feasible, while validating radiotherapy as a reasonable alternative in selected pts.