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A phase I study of carboplatin (Paraplatin) administered in two different dosing schedules (single dose every 4 weeks and weekly dosing) in combination with weekly irinotecan (CPT-11, Camptosar) was conducted in patients with relapsed or refractory advanced malignancies. Fifty-three patients with a variety of tumor types were randomly enrolled on the two different treatment regimens and have received a total of 163 cycles of treatment to date. Twenty-six patients received weekly irinotecan in combination with a single fixed dose of every-4-week carboplatin (arm 1). Initially, patients received irinotecan on days 1, 8, and 15, in combination with fixed-dose carboplatin at an area under the concentration-time curve (AUC) of 5.5 (Calvert formula) on day 1 every 28 days. Due to dose-limiting toxicities encountered at the first two dose levels, the protocol was amended to decrease the fixed dose of carboplatin to an AUC of 4.0 every 4 weeks. Dose-limiting toxicity was again encountered, so the day-15 dose of irinotecan was eliminated from the dosing regimen. The recommended phase II dose for heavily pretreated patients is irinotecan at 60 mg/m2 on days 1 and 8 in combination with carboplatin at AUC 4.0 on day 1 with cycles repeated every 28 days. Twenty-seven patients were treated with weekly irinotecan in combination with fixed-dose weekly carboplatin (arm 2). The initial dosing regimen consisted of irinotecan in combination with fixed-dose carboplatin at an AUC of 1.8 on days 1, 8, and 15, with treatment cycles repeated every 28 days. Due to the development of dose-limiting toxicities at the first two dose levels, the dosing regimen was subsequently amended to weekly irinotecan in combination with fixed-dose carboplatin at AUC 2.0 on days 1 and 8 only, and the dosing interval was shortened to every 21 days. With this amended regimen, the recommended phase II doses are irinotecan at 90 mg/m2 in combination with carboplatin at AUC 2.0 on days 1 and 8, with treatment cycles repeated every 21 days.