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Mitoxantrone (MTZ) and vinorelbine (VNR) have shown a good efficacy in advanced breast cancer. We conducted a phase I-II trial to determine the MTDs and best schedule of these drugs, in advanced breast cancer patients, when granulocyte-colony stimulating factor (G-CSF) support was given. The starting dose-intensity level was MTZ 3 mg/m2/week + VNR 15 mg/m2/week; dose was escalated at each step by 1 mg/m2/week for MTZ and 5 mg/m2/week for VNR, until dose limiting toxicity (DLT) developed in 33% or more of the patients at the first course. G-CSF 5 micrograms/kg/day d3-13 was administered at each cycle from dose level 2 on. For each dose step we planned 3 different schedules (a = total dose of MTZ on day 1; b = total dose d1 and 8; c = weekly schedule). At the time of this analysis (December 1993) 43 patients with locoregionally advanced or metastatic breast cancer have entered this study, 23 of whom had received prior chemotherapy other than adjuvant. Toxicity has been primarily hematologic. Non hematologic toxicity never caused interruption of dose escalation. Overall 8 patients developed DLT at the first course. Dose escalation was stopped at level 3 in patients receiving schedules a or b, and in those receiving schedule c the dose was escalated until level 5. The MTD was MTZ 6 mg/m2 and VNR 30 mg/m2 weekly. Age, dose level, and PS were found to be correlated with neutrophil and platelet nadirs, but dose level was the only independent variable predictive of myelotoxicity at multiple regression analysis. Forty-one patients were evaluable for response.(ABSTRACT TRUNCATED AT 250 WORDS)

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