Outcome of children and young adults with localized extremity rhabdomyosarcoma treated on Children's Oncology Group trials.

10006 Background: Extremity rhabdomyosarcoma (RMS) accounts for 15-20% of patients with localized RMS. The long-term survival and associated prognostic factors of extremity RMS patients treated on the contemporary Children’s Oncology Group (COG) trials have not been reported. Methods: Patients with localized extremity RMS enrolled on the D9602, D9803, ARST0331 and ARST0531 COG trials were analyzed. The Kaplan-Meyer method estimated event-free (EFS) and overall survival (OS). The Log-rank test and Cox regression were used to estimate the prognostic significance of age at diagnosis, sex, race, tumor site & size, IRS group, stage, histology, FOXO1 fusion status, anaplasia, lymph node involvement, delayed primary excision (DPE) and radiation on survival. Results: We identified 159 patients with localized extremity RMS; 108 (68%) were < 10 years at diagnosis, 84(53%) had primary tumor > 5 cm, and 35 (22%) and 98 (62%) had IRS group II and III disease. Histology was alveolar in 106 (67%), and 43 (27%) had regional lymph node involvement on imaging or pathology. Seventeen were treated on low-risk (LR) studies D9602 (N = 10) and ARST0331 (N = 7), whereas 142 were treated on intermediate-risk (IR) trials D9803 (N = 85) and ARST0531 (N = 57). Eighty patients (50%) underwent primary surgical excision and 121 (76%) received radiotherapy. DPE was attempted in 60 patients (38%), resulting in an R0 (microscopically negative) margin in 48 (80%). Relapse/progression occurred in 52 patients: metastatic 26 (50%), local 22 (42%), and combined 3(6%). The 5-year EFS and OS of the whole cohort were 62.6% (95% CI: 54%-71.2%) and 78.7%% (95%CI: 71.4%-85.9%). LR patients treated on D9602 and ARST0331 trials had comparable 5-year EFS (70% vs. 71.4%, p-0.90) and OS (90% vs. 85.7%, p-0.54), respectively, while IR patients had significantly better 5-year EFS (68.9% vs. 51%, p-0.023) and OS (86.2% vs. 64.4%, p-0.007) on D9803 trial than ARST0531 trial. The 5-year EFS and OS of IRS group III patients with DPE with R0 margins were comparable to IRS group II patients (70.4% vs. 66.6%) & (86.5% vs. 84.6%), respectively. On univariable analysis, age at diagnosis and sex were associated with EFS, while age at diagnosis, sex, tumor size, IRS group, stage and fusion status were associated with OS (p < 0.05). None of the analyzed factors demonstrated independent statistical association with EFS, whereas female sex was the only factor independently associated with OS [Hazard ratio (HR): 0.4, 95% CI 0.20-0.85)]. Conclusions: IR localized extremity RMS patients treated on ARST0531 had suboptimal outcome. Survival of IRS group III patients with R0 DPE was comparable to IRS group II patients. Females with localized extremity RMS had better OS than males. Clinical trial information: NCT00354835 ; NCT00003958 ; NCT00075582 ; NCT00002995 .