DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed solid tumor refractory to standard therapy or for which no known effective therapy exists

  • Brain tumors eligible

    • Histologic verification waived for brain stem gliomas
• Evaluable disease
• No bone marrow involvement

PATIENT CHARACTERISTICS:

Age:

• 1 to 21

Performance status:

• Karnofsky 50-100% (over age 10)
• Lansky 50-100% (age 10 and under)

Life expectancy:

• At least 8 weeks

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• Hemoglobin at least 8 g/dL

Hepatic:

• Bilirubin less than 1.5 mg/dL
• SGPT less than 5 times normal

Renal:

• Creatinine normal OR
• Glomerular filtration rate at least 70 mL/min

Other:

• No uncontrolled infection
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception during and for 6 months after study

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 6 months since prior autologous bone marrow transplantation (BMT) (not including stem cell rescue after high-dose chemotherapy)
• At least 1 week since prior growth factors
• No prior BMT with total body irradiation (stratum I)
• No prior BMT with or without total body irradiation (stratum 2)
• No prior allogeneic BMT (all strata)
• No concurrent sargramostim (GM-CSF)
• No other concurrent prophylactic growth factor support during the first course of therapy

Chemotherapy:

• At least 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas)
• No prior irinotecan
• No more than 2 prior multi-agent chemotherapy regimens (stratum 2)
• No other concurrent chemotherapy

Endocrine therapy:

• Concurrent dexamethasone allowed if on stable or decreasing dose for at least 2 weeks prior to study

Radiotherapy:

• At least 6 months since prior craniospinal radiotherapy or radiotherapy to 50% or more of the pelvis
• At least 6 weeks since other prior substantial bone marrow radiotherapy
• No prior central axis radiotherapy, pelvic radiotherapy, and/or total abdominal radiotherapy (stratum 2)

Surgery:

• Not specified

Other:

• Recovered from all prior therapy
• No other concurrent investigational agents
• Concurrent enzyme-inducing anticonvulsants (e.g., phenytoin, phenobarbital, carbamazepine) allowed if on stable dose for at least 2 weeks prior to study (stratum 3)
• Concurrent valproic acid allowed if combined with another enzyme inducing anticonvulsant drug (stratum 3)