OUTLINE: This is a dose escalation study. Patients are stratified according to concurrent enzyme-inducing antiepileptic drugs (EIAEDs)(yes vs no). Group A (without EIAEDs): Patients receive irinotecan IV over 90 minutes on day 1, followed by up to 3 weeks of rest. Group B (with EIAEDs): Patients receive the same treatment but dose escalation is performed in cohorts of 3 patients. The maximum tolerated dose (MTD) is defined as the dose below that at which 2 of 6 patients experience dose limiting toxicities. The Phase I MTD is the starting dose recommended for use in the Phase II portion of the study. Treatment continues every 3 weeks for up to 12 months in the absence of disease progression or unacceptable toxicity. Patients are followed every 2 months for 1 year, every 3 months for 1 year, every 4 months for 1 year, then every 6 months until disease progression. Patients are then followed every 4 months for survival.