Real World Outcomes of Metastatic Rhabdomyosarcoma in Children Treated With a Multimodal Protocol: A Single Center Experience

BACKGROUND AND AIMS: Metastatic rhabdomyosarcoma (RMS) at diagnosis has poor outcomes. We audited these outcomes in children at a tertiary sarcoma unit. METHODS: Children aged 15 years or younger with RMS at first diagnosis staged by FDG-PET CECT scan between January 2013 and December 2024 were retrospectively analyzed. Pulmonary, lymph node, and oligometastatic bone disease were treated with curative intent on a multimodal protocol comprising chemotherapy and local therapy to the primary and metastatic sites. RESULTS: Of 126 patients, 19% had isolated pulmonary, 81% had extrapulmonary metastases, with bone marrow involvement in 3.1%. After neoadjuvant chemotherapy in 73 patients (treated with curative intent), 74% had complete response (CR), 19% partial response (PR), 4% stable disease, and 3% progression. Local therapy to the primary was given to 68 patients (radiotherapy: 70.5%, surgery+radiotherapy: 22.1%, surgery: 7.3%), and metastatic sites were treated in 61.8%. At a median follow-up of 11 months (IQR: 3.31, 20.8), 2-year EFS and OS probabilities were 30.2% (95% CI: 19.8-41.2) and 44.4% (95% CI: 32.5-55.6), respectively; survival did not differ by metastasis site. Complete response at primary (HR: 0.09, 95% CI: 0.30-0.29, P<0.001), baseline tumor size ≥3.3 cm (HR: 4.93, 95% CI: 1.51-16.08, P=0.008), and bone marrow involvement (HR: 1.98, 95% CI: 1.01-3.91, P=0.050) affected EFS. CONCLUSIONS: Despite multimodal therapy, metastatic rhabdomyosarcoma continues to have poor outcomes. Tumor size ≥3.3 cm in oligometastatic disease and bone marrow involvement predicted poor prognosis, while complete primary site response after neoadjuvant chemotherapy was associated with improved survival.