Rhabdomyosarcoma (RMS) is one of the typical tumors of childhood and adolescence, but it is exceedingly rare in adults. Unfortunately, the treatment success achieved over the years for pediatric RMS has not translated into better cure rates for adults, who continue to have a very poor prognosis (overall survival rates of only 20–40%). To better characterize adult RMS, we performed an analysis of all RMS cases registered on the Surveillance Epidemiology and End Results (SEER) public-access database collected from various geographic areas in the United States from 1973 to 2005.

We analyzed 2600 patients, 1071 adults (> 19 years) and 1529 children (≤19 years). Tumors in adults were more likely to be at an unfavorable site (65% vs. 55%; P< 0.0001) and to have histologies that are unusual during childhood, particularly the pleomorphic subtype (19%) and not otherwise specified (43%). Regional and distant spread was not significantly higher in adults.

Adults had significantly worse outcome than children (5-year overall survival 26.6% and 60.5%, respectively; P< 0.0001). Adults had significantly worse outcome also analyzing subset of patients with similar tumors (i.e. same histotype, same stage). The most significant difference was in localized disease; 5-year overall survival rates were 82.2% and 46.8%, respectively (P < .0001). Multivariate analysis showed that age, histologic subtype, primary site location, stage, treatment with surgery, and treatment with radiation were significant predictors of survival. However, alveolar subtype and unfavorable primary site lost significance when analysis was restricted to adults.

In conclusion, our analysis confirmed that adult RMS was associated with a very poor outcome, especially in contrast to the significant improvements achieved in children treated contemporarily. The outcome for adults is consistently worse regardless of clinical characteristics, suggesting that factors other than an unfavorable clinical presentation might be involved in their unsatisfactory treatment results.