Event‐free survival in relapsed and refractory rhabdomyosarcoma treated on cooperative group phase II trials: A report from the Children's Oncology Group

Abstract Background Novel therapies are needed for relapsed and refractory rhabdomyosarcoma (RRMS). Phase II clinical trials in RRMS have typically utilized radiologic response as the primary activity endpoint, an approach that poses several limitations in RRMS. In this analysis, we aimed to estimate an event‐free survival (EFS) endpoint for RRMS that could be used as a benchmark for future studies. Procedure We performed a retrospective study of patients with RRMS enrolling on 13 single‐agent phase II Children's Oncology Group and legacy group trials from 1997 to 2016. All included trials used radiographic response as their primary activity endpoint. Six‐month EFS was estimated from time of trial enrollment with 95% confidence intervals. Clinical characteristics, including trial of enrollment, sex, age, race, histology, number of prior chemotherapies, and radiographic response were evaluated for their impact on 6‐month EFS. Results We identified 175 patients across 13 trials. The 6‐month EFS was 16.8% (11.6%–22.8%). No differences were seen in 6‐month EFS based on age, sex, race, or histology. There were nonsignificant trends toward improved 6‐month EFS for patients with less than or equal to two prior lines of therapy versus higher than two, for patients enrolled on trials that achieved their primary radiographic response endpoint versus trials that did not, and for patients who achieved complete or partial response compared to those achieving stable disease. Conclusions The prognosis of RRMS enrolled on single‐agent phase II trials is poor. This pooled 6‐month EFS of RRMS on single‐agent trials may be used as a RRMS‐specific benchmark for future single‐agent phase II trials.