The impact of pelvic radiotherapy on hematological toxicities in pediatric genitourinary rhabdomyosarcoma.

Abstract

Objectives: Hematological toxicities are a common sequelae of radiation therapy (RT), and pelvic RT is of particular concern as the pelvic marrow contributes nearly 50% of total body hematopoiesis. We evaluated the impact of pelvic RT on hematological toxicities in pediatric patients with pelvic genitourinary rhabdomyosarcoma (GU-RMS).

Methods: A secondary evaluation of 448 pediatric patients (53.8% male) with intermediate-risk RMS in the ARST0531 trial included 65 with pelvic GU-RMS (who received pelvic RT). Multivariable logistic regression was used to compare cytopenias and complications (febrile neutropenia, infectious complications) between GU-RMS and non-GU-RMS. Primary analysis assessed toxicities over the study period (weeks 1-43), with secondary analysis evaluating T1 (weeks 1-15), T2 (weeks 16-30), and T3 (weeks 31-43).

Results: GU-RMS patients did not have a significantly higher risk of cytopenias than non-GU RMS patients. Neutropenia was the most common, affecting 79.4% of subjects, with no significant difference between the GU (73.8%) and non-GU (80.4%) groups (OR 0.64, 95% CI 0.34-1.19, p = 0.16). Anemia rates were similar in the GU (36.9%; n = 24) and non-GU (35.2%; n = 135) groups (OR 0.96, 95% CI 0.54-1.70, p = 0.89). Thrombocytopenia occurred slightly more often in the GU group (33.8%) than the non-GU group (28.4%) but was not statistically significant (OR 1.49, 95% CI 0.81-2.73, p = 0.20). Pelvic RT for GU-RMS in T1 was linked to a significantly higher risk of thrombocytopenia compared to non-GU subjects (OR 2.79, 95% CI 1.25-6.23, p = 0.01), which declined over time (T2, T3). Rates of febrile neutropenia (3.1%-9.2%) and infectious complications (4.6%-15.4%) in GU patients did not differ significantly from those in non-GU cohorts (febrile neutropenia: 7.3%-13.05%; infectious complications: 5.5%-9.7%) across T1-T3.

Conclusions: Hematological toxicities were comparable between pediatric GU and non-GU RMS patients. Pelvic RT for GU-RMS increased the risk of early thrombocytopenia, which diminished over time.