The Prognostic Significance of Early Tumor Volume Change in Rhabdomyosarcoma

To describe early tumor volume change in patients with rhabdomyosarcoma (RMS) and investigate its association with overall survival (OS) and local failure.

This retrospective study included patients who received diagnoses of group III/IV RMS with available computed tomography and/or magnetic resonance imaging scans at 2 time points: (1) pretherapy and (2) early therapy (acquired during weeks 8-12 of chemotherapy). Relative volumetric change (RVC) was calculated as the percentage of (early therapy - pretherapy volume) / (pretherapy volume). Cox regression was used to identify variables associated with OS. The Fine-Gray model was used to estimate local failure.

Eligible patients (n = 55) had the following characteristics: median age at diagnosis, 9.6 years and median follow-up, 30.4 months. Most tumors were alveolar (61.8%), followed by embryonal (34.6%) and spindle cell/sclerosing (4%). The median RVC was -86.4% with larger decreases observed in alveolar versus nonalveolar RMS (-89.4% vs -69.8%, P = .043). For embryonal and spindle cell/sclerosing RMS, all of which were FOXO1 fusion negative, RVC was independently associated with OS (hazard ratio for every 50% reduction in RVC [HR_RVC], 0.5; 95% CI, 0.26-0.96; P = .037) and local failure (HR_RVC, 0.57; 95% CI, 0.33-0.99; P = .049). The predominant pattern of failure in embryonal and spindle cell/sclerosing RMS was local, and most were group III.

There was a greater reduction in tumor volume in alveolar versus nonalveolar RMS. Early tumor volume reduction was associated with OS and local failure in embryonal or spindle cell/sclerosing RMS, all of which were confirmed FOXO1 fusion negative and had higher incidence of local compared with distant failures.