Simvastatin With Topotecan and Cyclophosphamide in Relapsed and/or Refractory Pediatric Solid and CNS Tumors

The starting dose of simvastatin will be 140 mg/m\^2/dose BID for 21 days for the first group. Dose escalation for subsequent groups will be 180 mg/m\^2/dose BID, 225 mg/m\^2/dose BID, and 290 mg/m\^2/dose BID. If the maximum tolerated dose (MTD) has been exceeded at the first dose level, then the subsequent cohort of subjects will be treated at a dose of 100 mg/m2/dose BID (dose level 0). Simvastatin will be administered orally twice daily, approximately 12 hours apart. Feeding tube (nasogastric tube or gastrostomy tube, NOT a jejunum localized tube) administration is allowed. If a subject vomits a dose of simvastatin, it will not be repeated.

The dose of cyclophosphamide will be fixed at 250 mg/m\^2/dose. Cyclophosphamide will be administered intravenously over 30 minutes once daily for 5 days every 21 days.

The dose of topotecan will be fixed at 0.75 mg/m\^2/dose. Topotecan will be administered, after cyclophosphamide, intravenously over 30 minutes once daily for 5 days every 21 days.

Myeloid growth factor (G-CSF or pegylated G-CSF) will be initiated 24-48 hours after the completion of topotecan and cyclophosphamide for all subjects, which would be day 6 or 7. Myeloid growth factor should continue until the absolute neutrophil count is greater than 2,000/mm\^3