A prospective randomized trial comparing epirubicin monochemotherapy to two fluorouracil, cyclophosphamide, and epirubicin regimens differing in epirubicin dose in advanced breast cancer patients. The French Epirubicin Study Group The French Epirubicin Study Group carried out a randomized trial comparing epirubicin alone 75 mg/m2 with fluorouracil (5FU) 500 mg/m2, cyclophosphamide 500 mg/m2, and epirubicin 50 mg/m2 (FEC 50) and 5FU 500 mg/m2, cyclophosphamide 500 mg/m2, and epirubicin 75 mg/m2 (FEC 75) as first treatment for advanced breast cancer patients. Patients were stratified according to whether or not there were bone metastases only. Four hundred twelve patients entered this trial; 378 were assessable for tolerability and 365 for efficacy. The overall response rates were comparable between FEC 50 (44.6%) and FEC 75 (44.7%), but both were better than the epirubicin alone (30.6%) (P = .04 and P = .0006, respectively). The complete response rate was better in FEC 75 (15.5%) than in FEC 50 (7%) (P = .025) or epirubicin (4%) (P = .002). Similar results were obtained in the group of patients without bone-only metastases. No difference in the three treatments was observed in the patients with bone metastases only. Mean durations of response were similar in the three groups, being 412 days, 440 days, and 350 days for FEC 50, FEC 75, and epirubicin, respectively. Patients without previous adjuvant chemotherapy fared better than those with previous treatment (without anthracyclines). Tolerability was fair in the three groups. Overall, the epirubicin-alone group showed better tolerance than the two other groups, which did not differ significantly. Time to progression and survival were not different among the three groups, but more early relapses occurred in the epirubicin and FEC 50 groups; survival seemed to be better during the first 8 months in the FEC 75 group, and the survival difference between the epirubicin group and the FEC 75 group was of borderline significance. No difference in survival was observed between epirubicin- and FEC 50-group patients, even though the response rate was significantly worse in the monochemotherapy group. 