DISEASE CHARACTERISTICS: Histologically confirmed nonhematologic malignancy refractory to available therapies or for which no curative therapy exists Measurable or evaluable disease No active brain metastases, including evidence of cerebral edema by CT scan or MRI, progression from a prior imaging study, or any requirement for steroids or clinical symptoms of/from brain metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 3 months Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin less than 1.5 mg/dL ALT and AST less than 2 times upper limit of normal (ULN) (unless clearly related to hepatic metastases) Renal: Creatinine less than 1.5 times ULN Other: No other serious uncontrolled medical disorder or active infection that would preclude study No dementia or altered mental status that would preclude study Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 10 weeks after study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy No concurrent colony stimulating factors (e.g., filgrastim (G-CSF) or sargramostim (GM-CSF)) Chemotherapy: No prior topoisomerase I inhibitors (e.g., nitrocamptothecin, aminocamptothecin, irinotecan, or topotecan) At least 4 weeks since prior chemotherapy (at least 6 weeks since prior nitrosoureas, mitomycin, or carboplatin) No other concurrent chemotherapy Endocrine therapy: See Disease Characteristics At least 4 weeks since prior hormonal therapy No concurrent hormonal anticancer therapy Radiotherapy: At least 4 weeks since prior radiotherapy involving at least 30% of the bone marrow No concurrent radiotherapy Surgery: Not specified Other: No other concurrent experimental anticancer medication