Radiotherapy is Important for Local Control at Primary and Metastatic Sites in Pediatric Rhabdomyosarcoma

Purpose: The current recommended practice for pediatric patients with metastatic rhabdomyosarcoma includes full-dose radiotherapy to each metastatic site. We wished to question this practice, which can cause side-effects and is often logistically challenging, by studying the pattern of failure in our pediatric and teenage patient population. Methods and Materials: Our institution’s cancer registry was queried for patients diagnosed with rhabdomyosarcoma aged 18 or less from January 1990 until January 2014. Twenty-nine patients were found and, of these, six had metastatic disease. Five of the six were treated with standard chemotherapy together with radiotherapy to the primary and metastatic sites with doses and fractionation according to the site. Progression-free survival was calculated from the end of radiotherapy until radiological or pathological evidence of disease progression or death. Results: Median age was 13 years (range: 12-18). Three were girls. All had alveolar histology and unfavorable primary sites. Twelve metastatic sites were treated with radiotherapy. Doses used were 41.4 - 50.4 Gy in 1.8 Gy fractions for most sites, and 15 Gy in 1.5 Gy fractions for whole lung radiotherapy. The median number of sites treated per patient was two (range: 1 - 6). Median time to progression was 10.1 months (range: 1.9 - 15.7). Local control was 100% for all metastatic sites. Median overall survival (OS) was 31.8 months (range: 20.4 – 95.4 months). Three patients developed progressive disease outside the treated field. One patient died from a secondary hematological malignancy without evidence of disease progression. One patient remains progression-free at 88.6 months post-radiotherapy. Conclusions: Radiotherapy to metastatic disease sites prevented in-field progression in all five patients with metastatic alveolar rhabdomyosarcoma. However, failure at sites outside of the radiotherapy volume occurred in three of five of patients and overall survival was very poor despite aggressive treatment to all sites of disease. Radiotherapy has a role in metastatic disease, although future studies evaluating dose and fractionation are needed.