OUTLINE: This is a multicenter, dose-escalation study of irinotecan. Patients are stratified according to UGT1A1 genotype (high-risk [7/7 or 6/7 genotype AND bilirubin ≥ 0.6 mg/dL] vs low-risk [absence of high-risk criteria]) if a high-risk patient experiences a dose-limiting toxicity (DLT).