Analysis of local control outcomes and clinical prognostic factors in localized pelvic Ewing sarcoma patients treated with radiation therapy: A Report from the Children's Oncology Group.

<bold>Purpose: </bold>To identify potential clinical prognostic factors associated with a higher risk of local recurrence in localized pelvic Ewing sarcoma (ES) patients treated with radiation therapy.<bold>Methods: </bold>Data for 101 patients treated with definitive radiotherapy (RT) or both surgery and radiation (S+RT) to primary pelvic tumors on INT-0091, INT-0154, and AEWS0031 were analyzed. Imaging data for patients who did not receive radiation were not available for central review, so surgery alone patients were not included. Cumulative incidence rates for local failure at 5-years from time of local control were calculated accounting for competing risks.<bold>Results: </bold>The most common pelvic subsite was sacrum (44.6%). RT was utilized in 68% of patients and S+RT in 32%. The local failure rate was 25.0% for RT and 6.3% for S+RT (p=0.046). There was no statistically significant difference in local control modality by tumor characteristics. Tumors originating in the ischiopubic-acetabulum region were associated with the highest local failure incidence, 37.5% (p=0.02, vs. sacrum and iliac/buttock tumors), particularly those treated with RT (50.0%, p=0.06). A higher incidence of local failure was seen with each additional 100 mL of tumor at diagnosis (p=0.04). Multivariable analysis demonstrated RT alone (HR 5.1, p=0.04), tumor subsite (particularly ischiopubic-acetabulum tumors, HR 4.6, p=0.02), and increasing volume per 100 mL (HR 1.2, p=0.01) were associated with a higher incidence of local recurrence.<bold>Conclusions: </bold>Combination surgery and RT is associated with improved local control in patients with pelvic ES compared to definitive RT. Tumors involving the ischiopubic-acetabulum region and increasing tumor volume at diagnosis are associated with inferior local control. Tumor characteristics did not correlate with choice of local therapy modality suggesting an opportunity to develop best local therapy practices guidelines for future studies based on tumor features. [ABSTRACT FROM AUTHOR]