Excessive Treatment Failures in Patients With Parameningeal Rhabdomyosarcoma With Reduced-dose Cyclophosphamide and Delayed Radiotherapy.

Pediatric patients with parameningeal rhabdomyosarcoma and high-risk features are recommended to receive radiotherapy at initiation of protocol therapy due to concerns about the increased risk of local and leptomeningeal failure from treatment delay. We report our early experience on a multi-institutional prospective trial incorporating delayed primary site radiation and reduced dose cyclophosphamide in all patients with parameningeal tumors. We observed an excessive number of locoregional treatment failures following this approach and have subsequently amended our trial to move radiation therapy upfront for those patients with high-risk features. We suggest that investigators should be vigilant for treatment failure given our early prospective experience with delayed radiotherapy and reduced dose cyclophosphamide.