Can Response Outcomes Predict Survival in Paediatric Patients Receiving Treatment for Relapsed and Refractory Rhabdomyosarcoma? Results From the Living-REFoRMS Systematic Review.

The relationship between radiological response and survival outcomes has been studied in upfront treatment in paediatric rhabdomyosarcoma and adult cancer settings. However, the extent of the relationship between these outcomes is unknown in children and young people (CYP) with relapsed and refractory rhabdomyosarcoma. Studies included in the Living-REFoRMS systematic review were analysed using Pearson correlation and linear regression to assess the relationship between objective response rate (ORR) and disease control rate (DCR), and progression-free survival (PFS) and overall survival (OS). Post hoc sensitivity analyses were conducted to assess the impact of removing cohorts that only included one evaluable CYP with rhabdomyosarcoma. Thirty-one studies (18% of total Living-REFoRMS dataset) reporting 46 cohorts with a total of 419 evaluable CYP were eligible for this analysis. Forty-eight percent of cohorts included only one evaluable CYP with rhabdomyosarcoma. ORR and DCR were positively correlated with PFS (p < 0.0001). ORR and DCR were positively correlated with OS, though this was not statistically significant in ORR (p = 0.276). All correlations were statistically significant in the sensitivity analyses, highlighting the impact that cohorts including a single CYP with rhabdomyosarcoma evaluable for response had on the results. These results illustrate a positive correlation between tumour shrinkage and control, and the duration of survival in relapsed and refractory rhabdomyosarcoma. We encourage the reporting of both ORR and DCR (or the elements required to calculate these) by tumour type within study reports to facilitate these aspects of clinical decision making.