If 0/3 patients at any dose level experience a DLT, the dose of irinotecan will be escalated by 10 mg/m2 in the next dose level. If 1/3 patients at any dose level experience a DLT, the cohort will be expanded by 3 additional patients to 6 patients. If no additional patients develop DLT, the dose of irinotecan will again be escalated in the next cohort of 3 patients. If 2/3 or 2/6 patients develop DLT, then dose escalation will cease, and the previous dose will be declared the MTD.