Adolescents and young adults with rhabdomyosarcoma: A report from the Soft Tissue Sarcoma Committee of the Children's Oncology Group

Introduction: The impact of established prognostic factors on survival outcomes for childhood rhabdomyosarcoma (RMS) have not been well described in the adolescent and young adult (AYA) RMS patient population.

Methods: This is a retrospective analysis of patients with newly diagnosed RMS enrolled between 1997 and 2016 on seven previously reported Children's Oncology Group (COG) clinical trials. Demographics, clinical features, treatment details, and outcome data were collected. Five-year event-free survival (EFS) and overall survival (OS) were estimated for patients diagnosed at age 15-39 years and those diagnosed under age 15 years using the Kaplan-Meier method. Log-rank test was used to compare prognostic factors for EFS and OS. Factors significant in the univariable analysis were included in a Cox proportional hazards regression model. Nonsignificant covariates were removed from the multiple regression model.

Results: Total 2151 patients including 402 AYAs were analyzed. AYAs were more likely to present with primary tumors ≥5 cm in size, metastatic disease, alveolar histology, and have FOXO1 fusions compared to children. Five-year EFS for the AYA cohort was 44.2% versus 67% for children (p < .001), and 5-year OS was 52% for the AYA cohort versus 78% for children (p < .001). Multivariable analysis revealed tumor site, size and invasiveness, clinical group, and histology were prognostic in AYAs.

Conclusion: AYAs with RMS have a poorer prognosis compared to younger children due to multiple factors. Further research focused on AYAs to better understand RMS biology and improve treatments is critical to improve survival.