Pattern of relapse in pediatric localized extremity rhabdomyosarcomas correlated with locoregional therapies administered

Background: Treatment of extremity rhabdomyosarcomas (RMS) includes chemotherapy, surgery, and radiotherapy. Lymph node irradiation is recommended in the presence of regional node involvement at diagnosis. The aim of this study was to analyze the correlation between the pattern of relapse of non-metastatic extremity RMS and the initial therapies delivered. Methods: All patients with localized extremity RMS prospectively treated in France in the MMT-95 and RMS-05 protocols were selected. Extent of disease and pattern of relapse were evaluated by clinical examination and imaging. Results: We identified 59 patients with clinical characteristics corresponding to unfavorable prognostic factors. Twenty patients (34%) were considered to have lymph node involvement at diagnosis. Regional node biopsy was performed in 32 patients (54%) and modified the lymph node stage in 8 of the 59 patients (14%). Seventy-three percent of patients received radiotherapy. Fifty-two patients achieved first remission. Overall, 26 patients underwent complete tumor resection, 17 had R1 margins, and 5 were not operated due to early tumor progression. With a median follow-up of 82 months (range: 5–287), 18 relapses had occurred, at least locoregional in 12 cases. The 5‑year local and nodal control rates were 73% (63–86%) and 86% (77–95%), respectively. Five-year progression-free and overall survival were 57% (95%CI [45–72%]) and 70% (95%CI [58–84%]), respectively. Conclusion: The main sites of extremity RMS relapse are locoregional. Nodal failures in non-irradiated fields are not uncommon. We recommend systematic biopsy of in-transit nodes, especially in alveolar RMS and/or RMS with regional positive nodes at diagnosis to ensure their negativity.