Contribution of PET/CT to Prediction of Outcome in Children and Young Adults with Rhabdomyosarcoma

The purpose of this retrospective study was to evaluate the role of (18)F-FDG PET or PET/CT in the prediction of patient outcome in children and young adults affected by rhabdomyosarcoma. Methods: Forty-one patients with histology-proven rhabdomyosarcoma who underwent PET or PET/CT were identified (age range, 1-20 y; mean age +/- SD, 9.9 +/- 5.8 y). Tumor maximum standardized uptake value (SUV(max)) and visually rated metabolic activity, as well as the presence of metabolically active lymph nodes and distant metastases, were compared with event-free and overall survival. Multivariate Cox regression analyses were performed to compare the prediction of outcome according to metabolic tumor intensity in relation to established prognostic factors. Results: Kaplan-Meier analyses revealed a significantly shorter overall survival in primary tumors visually rated as highly metabolically active or with a ratio of SUVmax to SUV of the liver above 4.6. In addition, metabolically active lymph node and distant site involvement was indicative of significantly lower survival rates. On multivariate Cox regression analysis, the impact of intensity or SUV(max) of the primary tumor on outcome failed to attain significance, although PET performed better than some of the prognostic factors established in larger patient groups (P = 0.081). Conclusion: (18)F-FDG PET/CT is a valuable tool for initial staging in children affected by rhabdomyosarcoma. (18)F-FDG PET/CT may be an additional predictor of outcome and may be used to refine risk-adapted therapy. PET performed better than some established risk factors. The borderline significance level of primary tumor metabolism in multivariate testing may be an effect of the limited sample size. Further prospective evaluations are warranted.