(P 304) LOCAL CONTROL FOR PEDIATRIC RHABDOMYOSARCOMA OF THE EXTREMITIES. IS RADIOTHERAPY ALWAYS REQUIRED AFTER ADEQUATE SURGICAL RESECTION?

Objective: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and young adults. Typically, treatment involves a multimodal approach, with radiotherapy (RT) being a standard choice alongside surgical resection for local control, particularly in cases harboring fusions involving FOXO1. However, the long-term consequences of offering RT especially to the extremity in children can be significant including growth delay, contracture, arthritis, and secondary malignancy. Herein, we report the outcome of 10 consecutive patients with extremity RMS from two high-volume institutions who did not receive RT

Methods: After regulatory approval, data from patients who were diagnosed between 2008-2023 with extremity RMS and did not receive RT from 2 institutions (Sickkids and Princess Margaret Cancer Center) were retrospectively extracted from the CanSaRCC Database and reviewed (Canadian Sarcoma Research and Clinical Collaboration) under the CanSaRCC Consortium Agreement. Data collection included demographics, genetics (somatic, germline), location and size of primary tumor, fusion and metastatic status, chemotherapy, surgery (type, margin status) and post-resection overall (OS) and event-free-survival (EFS).

Results: Ten patients with a median age of 5.0 years (range 0.25-10.0) presented with RMS – see table 1 for demographics and treatment details. All patients received chemotherapy and resection of primary tumor. 9/10 pts had an R0 resection (Minimal margins size range of 0.7-10mm, median – 2.5mm), 6 after receiving neo-adjuvant chemotherapy. None of the patients received RT to primary tumor. Despite the absence of adjuvant RT to the primary tumor site and receipt of neo-adjuvant chemotherapy, 90% (n=9) of patients did not have local failure; the single patient with local failure (21 months from diagnosis) was subsequently salvaged with RT and further chemotherapy

Conclusion: In a high-volume pediatric sarcoma center with orthopedic oncology expertise, local control in extremity RMS can be achieved with surgery and chemotherapy alone