Early response as assessed by anatomic imaging does not predict failure-free survival among patients with Group III rhabdomyosarcoma: A report from the Children's Oncology Group

Background The prognostic significance of response to induction therapy for rhabdomyosarcoma (RMS) by anatomic imaging [computerised tomographic (CT) or magnetic resonance imaging (MRI) scan] is controversial. We previously reported no relationship between early response and failure-free survival (FFS) on Intergroup Rhabdomyosarcoma Study (IRS)-IV. We repeated the same analysis using a more recent clinical trial as an independent cohort of patients with non-metastatic, initially unresected RMS. Methods A total of 338 patients enrolled in Children's Oncology Group (COG) study D9803 met the inclusion criteria for this analysis: (1) non-metastatic, initially unresected (Group III); (2) embryonal (ERMS) or alveolar (ARMS) histology; (3) documented protocol week 12 response to induction chemotherapy (excluding progressive disease) based on anatomic imaging (CT/MRI) and (4) documented protocol therapy beyond week 12. Response at week 12 was determined by the treating institution as complete response (CR), partial response (PR) or no response (NR). FFS was estimated using the Kaplan-Meier method and comparisons between patient subsets were made using the log-rank test. Results Overall objective response rate (CR + PR) at week 12 of therapy was 85% and was similar between 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 response within either histology subset (p = 0.89 and p = 0.08, respectively). Conclusions These findings provide additional evidence that anatomic imaging to assess early response to therapy among patients with RMS does not predict outcome and has questionable use in tailoring subsequent therapy.