DISEASE CHARACTERISTICS: Histologically confirmed malignant solid tumor that is refractory to conventional therapy or recurrent neuroblastoma treated with myeloablative therapy and autologous stem cell transplant in second complete or partial response Bone marrow metastases with granulocytopenia, anemia, and/or thrombocytopenia are eligible

PATIENT CHARACTERISTICS: Age: Under 21 at diagnosis Performance status: CCG 0-2 Life expectancy: At least 2 months Hematopoietic: Absolute neutrophil count at least 750/mm3 Platelet count at least 50,000/mm3 Hemoglobin at least 7.0 g/dL Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT and SGPT less than 2.5 times normal Renal: Creatinine no greater than 1.5 g/dL OR Creatinine clearance at least 50 mL/min OR Radioisotope GFR at least 50 mL/min Other: Seizure disorders controlled with anticonvulsants allowed No CNS toxicity greater than grade 2 Not pregnant Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 1 month since prior autologous stem cell transplantation No prior allogeneic transplantation Chemotherapy: At least 2 weeks since prior chemotherapy (4 weeks for nitrosourea) and recovered No other concurrent chemotherapy Endocrine therapy: No concurrent immunomodulating agents (including steroids) Concurrent corticosteroid therapy for increased intracranial pressure allowed Concurrent dexamethasone for CNS tumor allowed Radiotherapy: At least 2 weeks since prior radiotherapy Concurrent radiotherapy to localized lesions allowed Surgery: Not specified Other: At least 2 weeks since prior retinoids Prior isotretinoin or 9-cis-retinoic acid allowed