Impact of Rhabdomyosarcoma Treatment Modalities by Age in a Population-Based Setting

Purpose: Rhabdomyosarcoma (RMS) has a worse prognosis in adults than in children, but there is evidence of a better outcome in the former if treated using a pediatric-like approach. This study describes treatment for RMS in patients more than 10 years old and examines to what extent treatment contributes to explain the different age-related survival observed and to what extent treatment centers impact treatment appropriateness. Methods: A retrospective population-based study was developed considering 104 RMS cases (excluding the pleomorphic subtype) diagnosed in Italy between 2000 and 2015. Patients were grouped by age (10-19 vs. 20-60 years old) and scored according to whether or not their chemotherapy was consistent with the schemes used in pediatric protocols (score 1=chemotherapy in line with pediatric protocols). Treatment centers were grouped according to whether or not they have a pediatric-dedicated unit affiliated to the national pediatric oncology network (Associazione Italiana Ematologia Oncologia Pediatrica [AIEOP]). Results: Older patients were more likely to have tumors at unfavorable sites (p=0.045). A treatment score of 1 was assigned to 85% of younger patients, but only to 32% of older patients (p < 0.001). Furthermore, the proportion of score 1 was higher in younger patients treated in centers with an AIEOP Unit. A multivariate model confirmed age as a significant prognostic factor (Hazard rate ratio [HR]=2.06; p=0.04) and showed a significant impact of treatment on survival (HR=2.13; p=0.03). Conclusions: Adult RMS patients are still relatively unlikely to be treated with pediatric protocols and in centers with a pediatric oncology expertise. This may explain the survival gap between older and younger patients.