Tumor volume and patient weight as predictors of outcome in children with intermediate risk rhabdomyosarcoma: a report from the Children's Oncology Group

Background: The objectives of this study were to compare tumor volume and patient weight versus traditional factors of tumor size (greatest dimension) and patient age and to determine which parameters best discriminated outcome among pediatric patients with intermediate-risk rhabdomyosarcoma (RMS).

Methods: Complete information was available for 370 patients with nonmetastatic RMS who were enrolled in the Children's Oncology Group (COG) intermediate-risk study D9803 (1999-2005). The Kaplan-Meier method was used to estimate survival distributions. A recursive partitioning model was used to identify prognostic factors that were associated with event-free survival (EFS). Cox proportional hazards regression models were used to estimate the association between patient characteristics and the risk of failure or death.

Results: For all patients with intermediate-risk RMS, a recursive partitioning algorithm for EFS suggested that prognostic groups should be defined optimally by tumor volume (with a transition point at 20 cm(3) ), patient weight (with a transition point at 50 kg), and embryonal histology. Tumor volume and patient weight added significant outcome information to the standard prognostic factors, including greatest tumor dimension and patient age (P = .02). The ability to resect the tumor completely was not associated significantly with the size of the patient, and patient weight did not significantly modify the association between tumor volume and EFS after adjustment for standard risk factors (P = .2).

Conclusions: The factors that had the strongest association with EFS were tumor volume, patient weight, and histology. On the basis of regression modeling, tumor volume and patient weight were superior predictors of outcome compared with greatest tumor dimension and patient age in children with intermediate-risk RMS. The current results indicated that the prognostic performance of tumor volume and patient weight should be assessed in an independent prospective study.