Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents aged <20 years; its etiology remains largely unknown. It is believed that embryonal (ERMS) and alveolar rhabdomyosarcoma (ARMS), the most common subtypes, arise through distinct biologic mechanisms. The authors of this report evaluated incidence and survival trends by RMS demographic subgroups to inform future etiologic hypotheses.

Incidence and survival trends in RMS among children and adolescents aged <20 years were analyzed using data from the Surveillance, Epidemiology, and End Results Program. Frequencies, age‐adjusted incidence and survival rates, and joinpoint regression results, including annual percentage change (APC) and 95% confidence interval (CI), were calculated.

Between 1975 and 2005, the incidence of ERMS was stable, whereas a significant increase in the incidence of ARMS was observed (APC, 4.20%; 95%CI, 2.60%‐5.82%). This trend may have been attributable in part to shifts in diagnosis, because a significant negative trend in RMS, not otherwise specified was observed concurrently. A bimodal age peak for ERMS was observed, with the second, smaller peak in adolescence noted for males only; ARMS incidence did not vary by age or sex. Five‐year survival rates for RMS and ERMS increased during the period from 1976 to 1980 (52.7% and 60.9%, respectively) to the period from 1996 to 2000 (61.8% and 73.4%, respectively), whereas there was little improvement for ARMS (40.1% and 47.8%, respectively).

Observed differences in incidence and survival for 2 major RMS subtypes across sex and age subgroups further supported the hypothesis that there are unique underlying etiologies for these tumors. Exploration of these differences presents an opportunity to increase current knowledge of RMS. Cancer 2009. © 2009 American Cancer Society.