 Treatment: Patients in this study will receive irinotecan and Mytomycin C in one of two treatment schedules. Both drugs will be administered in patients through an intravenous infusion. A computer will randomly assign patients to a treatment group. Group one will receive Mytomycin C on day 1 and irinotecan on days 2 and 9. Group two will receive Mytomycin C on days 1 and 8 and irinotecan on days 2 and 9. After day 9, patients in both groups will not be given any study drugs for almost three weeks to complete a four week cycle. Several tests and exams will be given throughout the study to closely monitor patients. Patients will continue receiving the study drugs until they experience disease growth or unacceptable side effects. 