Rhabdomyosarcoma in Children and Adolescents: Patterns and Risk Factors of Distant Metastasis

OBJECTIVE. The objective of this study is to evaluate patterns of distant metastasis and identified factors that may increase the risk of distant metastasis in pediatric patients with rhabdomyosarcoma. MATERIALS AND METHODS. This retrospective study included 69 patients (age, <= 20 years) who had rhabdomyosarcoma diagnosed between January 2000 and February 2016. Various imaging features, including distant metastasis, were evaluated on initial and follow-up imaging studies. Differences in the distribution of distant metastasis on the basis of the primary location were analyzed. Logistic regression analysis was performed to identify factors associated with distant metastasis. RESULTS. Twenty-six of the 69 patients (37.7%) had distant metastasis. Nineteen of the 26 patients had distant metastasis noted at initial presentation, and 15 of the 26 patients had new metastasis noted during follow-up. The most common site of metastasis was bone (n = 14), followed by lung (n = 12) and distant lymph nodes (n = 9). Lymph node metastasis more frequently developed in patients with primary rhabdomyosarcoma in an extremity than in patients with primary rhabdomyosarcoma that developed at other sites (p = 0.003). Of 15 patients who had metastasis during follow-up, nine (60%) did not appear to have simultaneous locoregional recurrence at the time of the discovery of distant metastasis. Older age at presentation and unfavorable sites of the primary tumor were significantly associated with distant metastasis in multivariate analysis. CONCLUSION. Distant metastasis of rhabdomyosarcomas in pediatric patients showed different patterns according to the location of the primary tumor and even occurred without local recurrence.