OUTLINE: Patients are stratified based on their use/kind of anticonvulsant drugs. This stratification yields two arms for this study. Arm I consists of patients who use anticonvulsant drugs that induce hepatic metabolic enzymes. Arm II consists of patients who use anticonvulsant drugs that cause modest to no induction of hepatic metabolic enzymes or no anticonvulsant drug. Three patients in each arm receive irinotecan by 90-minute IV infusions every week for 4 weeks, followed by a 2 week rest period. The dose is escalated for the next cohort of 3 patients in the absence of unacceptable dose limiting toxicity. The 6 week course is repeated until unacceptable toxicity or disease progression. Once the maximum tolerated dose has been established for each arm, additional patients are treated at that dose level. Patients are followed every 2 months.