Phase I S tudy o f a n O ral F ormulation o f Z D9331 A dministered Daily f or 2 8 D ays

Purpose: To define the maximum-tolerated dose and dose-limiting toxicities (DLTs) of an oral formulation of ZD9331, a novel thymidylate synthase inhibitor that is not a substrate for folylpolyglutamate synthase. Patients and Methods: Patients had Cancer and Leukemia Group B performance status < 2 and refractory solid tumors. Initially, patients received ZD9331 daily for 2 weeks, with the duration of treatment escalated to a maximum of 4 weeks, followed by a 2-week rest period. Once the maximum-tolerated duration of treatment was determined, the dose of ZD9331 was increased until DLT occurred. Results: Fifty-five patients were enrolled at eight dose levels. The DLTs were thrombocytopenia and neutropenia. At 3 mg/d, two of 19 patients developed DLT; one patient had grade 3 thrombocytopenia and grade 4 neutropenia, and the other patient had grade 3 thrombocytopenia only. Anemia was common, with a median hemoglobin nadir of 75% of baseline, before recovery or transfusion. The apparent oral clearance of ZD9931 was 11.6 6.3 mL/min. Dose-limiting myelosuppression was associated with both an increased 24-hour ZD9931 concentration and blood urea nitrogen. Conclusion: The recommended phase II dose on this schedule is 3 mg/d for 4 weeks, followed by a 2-week rest period. ZD9331 seems to have a manageable toxicity profile, although it should be used with caution in patients with renal impairment. J Clin Oncol 21:1859-1865. © 2003 by American Society of Clinical Oncology.