Peripheral Stem Cell Transplantation Plus Chemotherapy in Treating Patients With Malignant Solid Tumors

OBJECTIVES: * Determine whether autologous transplantation of mobilized CD34+ peripheral blood stem cells (PBSC) can provide complete hematologic reconstitution after myeloablative chemotherapy comprising etoposide (VP-16) and carboplatin (CBDCA) in patients with metastatic or recurrent rhabdomyosarcoma, neuroblastoma, Ewing's sarcoma/primitive neuroectodermal tumor, germ cell tumors, childhood brain tumors, or hepatoblastoma. * Determine the frequency and yield of CD34+ PBSC and granulocyte-macrophage colony-forming units (GM-CFU) that are mobilized, harvested, and purified after a single priming course of high-dose cyclophosphamide (CTX) followed by filgrastim (G-CSF). * Correlate the number of CD34+ cells and GM-CFU in the autologous PBSC graft with time to engraftment of white blood cells, neutrophils, and platelets in these patients. * Determine the optimal day of PBSC harvest after a single priming course of high-dose CTX and G-CSF in these patients. * Determine whether CD34+ PBSC rescue and daily post-transplantation G-CSF decrease the time to hematopoietic recovery after high-dose VP-16 and CBDCA compared to historical results achieved in similar patients rescued with bone marrow. * Compare the tumor cell content of marrow, mobilized blood, and purified CD34+ PBSC graft preparations. * Determine the optimal timing of PBSC mobilization and harvest in relation to extent of prior chemotherapy in these patients. * Determine the feasibility of a single leukapheresis for PBSC harvest in children. * Determine the toxic effects of this regimen in these patients. * Determine the antitumor activity of this regimen in these patients. OUTLINE: This is a dose-escalation study of cyclophosphamide. Mobilization/harvest: Patients receive cyclophosphamide IV over 90 minutes on day 0 and filgrastim (G-CSF) subcutaneously or IV over 30 minutes on days 2-15 or until blood counts recover. Peripheral blood stem cells (PBSC) are harvested and selected for CD34+ cells on day 15. Bone marrow is also harvested in case insufficient PBSC are harvested. Preparative regimen/transplantation: Patients receive carboplatin IV over 1 hour and etoposide IV continuously on days -6 to -4. Cyclophosphamide is administered IV over 1 hour on days -3 and -2 or IV continuously on days -3 and -2, -4 to -2, -5 to -2, or -6 to -2. PBSC or bone marrow is reinfused on day 0. Cohorts of 3-10 patients receive escalating doses of cyclophosphamide until the maximum tolerated dose (MTD) is determined. The MTD is defined as the highest dose at which 20% of patients experience dose-limiting toxicity. At least 6 additional patients receive cyclophosphamide at the MTD. PROJECTED ACCRUAL: A minimum of 36 patients will be accrued for this study.