Prognostic role of bone erosion in orbital RMS: a report from the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG).

Orbital rhabdomyosarcoma (RMS) typically remains confined to the orbital cavity and has a favorable prognosis. However, when the tumor erodes the orbital bone, it may resemble parameningeal RMS (PM-RMS) and require more aggressive treatment. Current treatment protocols do not account for varying degrees of bone erosion (BE), which complicates risk classification and treatment decisions. To address this, we analyzed 199 patients with orbital RMS included in the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) protocol, categorizing BE into minimal (bone thinning), moderate (focal lysis), and extensive (complete cortical destruction). BE was observed in 27.6% of patients, with 13.6% classified as minimal, 3.5% as moderate, and 10.6% as extensive. Extensive BE was associated with larger tumors (>5 cm) and invasive characteristics. After a median follow-up of 70.4 months, 5-year event-free survival (EFS) and overall survival (OS) rates were 76% and 92%, respectively. Patients without BE had significantly better OS (95% vs. 81%) but not EFS. Extensive BE was associated with worse outcomes compared to no/minimal/moderate BE, with EFS of 57.1% vs. 78.1% and OS of 71.1% vs. 94%. Patients with extensive BE experienced more frequent relapses, particularly in the central nervous system or meninges. These findings suggest that only patients with orbital RMS and extensive BE should be classified as PM and treated with intensified protocols