- History of untreated CNS tumor involvement. Extradural masses which have not invaded the brain parenchyma (as is commonly observed in Ewing's sarcoma family of tumors) or parameningeal tumors (as is commonly observed in rhabdomyosarcoma) without evidence for leptomeningeal spread will not render the patient ineligible. Patients with previous central nervous system (CNS) tumor involvement that has been treated and has been stable for at least 6 weeks are eligible.