Objective: In breast cancer the efficacy of epirubicin-based chemotherapy is possibly related to the actual dose intensity applied. We retrospectively determined the administered dose intensity and the relative toxicity and efficacy of an epirubicin-containing regimen in patients with primary or metastatic breast cancer. Patients and Methods: Fluorouracil, epirubicin, and cyclophosphamide (FEC) were either given at a standard dose of 500/50/500 mg/m(2) (FE50C) or at an intensified dose of 500/75/500 mg/m(2) (FE75C) every 3 weeks. Of the 66 patients treated, 63 were evaluable; 43 had metastatic breast cancer, and 20 patients with an increased risk of relapse received FEC as an adjuvant treatment. Results: Dose intensity and absolute dose of adjuvant treatment were 81 and 70% for FE50C and 96 and 88% for FE75C In metastatic breast cancer, the dose intensity for FE50C was 94% and for FE75C 92%. In a retrospective comparison, the 4-year overall survival following adjuvant FE50C and FE75C was 40 and 48%, respectively (p = 0.47). The dose intensification led to a higher response rate of 34 vs. 44%. There were no significant differences in response duration and survival time. The toxicity profiles were comparable between FE50C and FE75C Conclusions: In genera I, the doses applied were lower than initially planned. Higher doses of epirubicin did not result in a significant increase of toxicity. Despite the limitations of a retrospective analysis, our observations support the importance of adherence to the planned dose intensity as a prerequisite for optimal treatment of patients suffering from breast cancer. As our results could be related to selection bias, dose-intensified anthracycline-containing regimens should be further evaluated in prospective trials. Copyright (C) 2001 S. Karger AG, Basel.