PURPOSE: Theoretical considerations and clinical experience suggest that dose-dense chemotherapy may be superior to other approaches using the same drugs. We studied a dose-dense combination of doxorubicin and cyclophosphamide, with or without fluorouracil, as adjuvant therapy. PATIENTS AND METHODS: Patients with resected breast cancer were treated if they were node-positive and estrogen receptor–negative, positive for overexpression of Her-2-neu, or had four or more involved nodes. Doxorubicin was given weekly to a total dose of 480 mg/m2. Cyclophosphamide 60 mg/m2 was given daily by mouth during the period of doxorubicin treatment. The first 30 patients received fluorouracil at 300 mg/m2/wk intravenously concurrently with doxorubicin administration. In the last 22, it was omitted because of symptomatic hand-foot syndrome in the majority of patients. Filgrastim (granulocyte colony-stimulating factor [G-CSF]) was administered during chemotherapy every day except the day of intravenous administration and continued until 1 week after the completion of the chemotherapy. RESULTS: Between October 20, 1992, and June 10, 1997, we enrolled 52 patients. The mean delivered dose-intensity for doxorubicin was 18.6 mg/m2/wk. Hospitalization was required in 6% of patients for reversible febrile neutropenia. There were no acute treatment-related deaths, but one patient subsequently died of acute leukemia with a characteristic translocation for anthracycline-related exposure. At 5 years, the event-free survival was 86% for all patients (95% confidence interval, 75% to 95%). CONCLUSION: Continuous dose-dense chemotherapy with G-CSF support produced encouraging results, which seem to be superior to those expected with “standard” doxorubicin and cyclophosphamide chemotherapy. It deserves a test in the form of a randomized trial where this approach to anthracycline-based treatment is compared with intermittent administration.