DISEASE CHARACTERISTICS:

• Histologically confirmed advanced solid tumors, including brain tumors and lymphomas, that have failed standard therapy (surgery, radiotherapy, endocrine therapy, or chemotherapy) or for which no standard therapy exists

  • Histology requirement waived for brain stem gliomas

PATIENT CHARACTERISTICS:

Age:

• 21 and under at diagnosis

Performance status:

• ECOG 0-2

Life expectancy:

• At least 8 weeks

Hematopoietic:

• Absolute neutrophil count at least 750/mm^3
• Platelet count at least 75,000/mm^3
• Hemoglobin at least 8.5 g/dL

Hepatic:

• Bilirubin no greater than 1.5 mg/dL
• SGOT or SGPT no greater than 2.5 times upper limit of normal (ULN) (5 times ULN if liver metastases)

Renal:

• Creatinine no greater than 1.5 times ULN OR
• GFR at least 70 mL/min

Other:

• Not pregnant or nursing
• Negative pregnancy test
• No history of severe or life-threatening hypersensitivity to camptothecin analogs
• HIV negative
• No other concurrent severe or uncontrolled medical illness
• No systemic infection

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Recovered from prior immunotherapy

Chemotherapy:

• See Disease Characteristics
• Recovered from prior chemotherapy

Endocrine therapy:

• See Disease Characteristics

Radiotherapy:

• See Disease Characteristics
• At least 4 weeks since prior extensive radiotherapy involving cranial, whole pelvic, or at least 25% of bone marrow reserve
• Recovered from prior radiotherapy
• Concurrent localized radiotherapy for pain allowed

Surgery:

• See Disease Characteristics
• Recovered from prior surgery

Other:

• No other concurrent antitumor therapy
• No concurrent drugs that induce or inhibit CYP3A enzyme