Group, Children's Oncology

10012 Background: The prognostic significance of response to induction therapy for rhabdomyosarcoma (RMS) by anatomic imaging (computerized tomographic [CT] or magnetic resonance imaging [MRI] scan) is controversial. We previously reported no relationship between early response and failure-free survival (FFS) for patients on IRS-IV. We repeated the same analysis using an independent cohort of patients with non-metastatic, initially unresected RMS treated on a more recent clinical trial. Methods: A total of 338 patients enrolled in Children’s Oncology Group study D9803 met the following inclusion criteria for this analysis: 1) non-metastatic, initially unresected (Group III); 2) embryonal (ERMS) or alveolar (ARMS) histology; 3) documented response to induction chemotherapy (excluding progressive disease) based on anatomic imaging; and 4) documented therapy beyond week 12. Response at week 12 was determined by the treating institution as complete response (CR, complete resolution), partial response (PR, decrease of >= 50% of the sum of the products of maximum perpendicular diameters), or no response (NR, between 50% reduction and 25% increase in the sum of the products of maximum perpendicular diameters). FFS was estimated using the Kaplan-Meier method, and comparisons between groups were made using the log-rank test. Results: Overall objective response rate (CR+PR) at week 12 of therapy was 85%, with similar responses for ERMS and ARMS. FFS was similar among all patients with CR, PR, or NR (p=0.49). Restricting the analysis to either ERMS or ARMS, there was no difference in FFS by histology (p=0.20 and p=0.45, respectively). Conclusions: These findings provide additional evidence that anatomic imaging assessment of early response to therapy among RMS patients does not predict outcome and should not be used to tailor subsequent therapy. Clinical trial information: NCT00003958. [Table: see text]