Phase I trial of high-dose mitoxantrone plus cyclophosphamide and filgrastim in patients with advanced breast carcinoma.

Purpose: To determine the maximum-tolerated dose (MTD) of mitoxantrone that could be safely used in combination with cyclophosphamide and filgrastim in patients with advanced breast carcinoma.
Patients and Methods: Twenty-seven patients with metastatic (n = 24) or locally advanced (n = 3) breast carcinoma received escalating doses of mitoxantrone (16, 20, 24, 28, or 32 mg/m2) plus cyclophosphamide at one of three dose levels: group 1, 1,200 mg/m2; group 2, 2,400 mg/m2; and group 3,600 mg/m2. All patients also received filgrastim 5 micrograms/kg administered subcutaneously beginning on day 2 and continuing until the post-nadir absolute neutrophil count (ANC) was > or = 10,000/microL. Treatment was repeated every 3 weeks if the ANC was > or = 2,000/microL and platelet count > or = 90,000/microL for a maximum of six cycles. Dose escalation occurred within each group if zero of three or one of four patients had dose-limiting toxicity during the first cycle.
Results: The MTD of mitoxantrone was 24 mg/m2 in group 1, less than 16 mg/m2 in group 2, and 28 mg/m2 in group 3. Neutropenia was dose-limiting, and cumulative neutropenia and thrombocytopenia occurred with continued therapy. Nonhematologic toxicity consisted predominantly of nausea, vomiting, alopecia, and fatigue. Three patients (11%) had a > or = 10% decrease in the left ventricular ejection fraction (LVEF), one patient (4%) had a decrease in the LVEF below normal, and none developed clinical congestive heart failure. Of patients with stage IV breast carcinoma who had not received prior chemotherapy for advanced disease, objective responses occurred in nine of 20 (45%), and the median response duration was 5 months.
Conclusion: In combination with 600 mg/m2 of cyclophosphamide and filgrastim, the MTD of mitoxantrone is 28 mg/m2, a dose that is approximately twofold to 2.8-fold higher than the conventional dose used without a hematopoietic growth factor.