Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically proven recurrent anaplastic oligodendroglioma or
anaplastic mixed oligoastrocytoma following primary surgery and radiation therapy Tumors
for anaplastic mixed oligoastrocytoma must contain at least 25% oligodendroglial elements
Tumors must be clinically aggressive for patients with only 1 anaplastic feature Prior low
grade oligodendrogliomas or oligoastrocytomas undergoing repeat biopsy following clinical
or radiological progression are eligible Bidimensionally measurable and progressive
lesions by CT or MRI

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-3 Life expectancy:
Not specified Hematopoietic: Absolute granulocyte count at least 1,500/mm3 Platelet count
at least 100,000/mm3 Hepatic: Not specified Renal: Creatinine normal Other: Not pregnant
or nursing Fertile patients must use effective contraception No prior malignancies except
curatively treated carcinoma in situ of the cervix or nonmelanoma skin cancer No other
serious illness or medical condition No active uncontrolled infection No history of
neurologic or psychiatric disorder

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 6 weeks
since chemotherapy No more than 1 prior chemotherapy regimen No prior camptothecin
derivatives Endocrine therapy: At least 2 weeks on stable steroid therapy, if necessary
Radiotherapy: At least 2 months since prior radiotherapy No prior radiation therapy for
recurrent disease Surgery: At least 6 weeks since prior surgery (except biopsy only) Prior
surgery for recurrent disease allowed (including stereotactic biopsy or partial resection)
Other: No concurrent experimental drugs or anticancer therapy