Prognostic significance of tumor response at the end of therapy in group III rhabdomyosarcoma: A report from the children's oncology group

Purpose: Some patients with rhabdomyosarcoma (RMS) achieve less than a complete response (CR) despite receiving all planned therapy. We assessed the impact of best response at the completion of all therapy on patient outcome. Patients and Methods: We studied 419 clinical group III participants who completed all protocol therapy without developing progressive disease for Intergroup Rhabdomyosarcoma Study (IRS) IV. Response (complete resolution [CR], partial response [PR; ≥ 50% decrease], or no response [NR; < 50% decrease and < 25% increase]) was determined by radiographic measurement and categorized by the best response. Results: At the end of therapy, 341 participants (81%) achieved a best response of CR and 78 (19%) had a best response of PR/NR. Five-year failure-free survival was similar for participants achieving CR (80%) and PR/NR (78%). After adjustment for age, nodal status, primary site, and histology, there was no significant indication of lower risk of failure (hazard ratio [HR], 0.77; 95% CI, 0.46 to 1.27; P = .3) nor death (HR, 0.63; 95% CI, 0.36 to 1.09; P = .1) for CR versus PR/NR participants. Seventeen participants with a best response of PR/NR had surgical procedures; eight (50%) of 16 with available pathology reports had residual viable tumor and only three achieved a complete resection. Resection of residual masses was not associated with improved outcome. Conclusion: CR status at the end of protocol therapy in clinical group III participants was not associated with a reduction of disease recurrence and death. Aggressive alternative therapy may not be warranted for RMS patients with a residual mass at the end of planned therapy.