Two randomized trials evaluated the effect of 6 courses of anthracycline-based chemotherapy in early breast cancer. A total of 1146 patients were included: 311 high-risk node-negative premenopausal patients and 835 high-risk node-negative or node-positive postmenopausal patients. Patients were randomized after surgery to receive either no chemotherapy (control group) or 6 courses of anthracycline-based chemotherapy (CT group). Postmenopausal patients received adjuvant tamoxifen for at least two years. Radiotherapy was delivered after completion of chemotherapy in the CT group. The 10-year disease-free survival (DFS) rates were 60% in the control group and 65% in the CT group (log-rank test, p = 0.01). The 10-year distant metastasis rates were 28% and 23% (p = 0.02), and the 10-year local recurrence rates were 12% and 10%, respectively (p = 0.24). Chemotherapy was significantly less effective in post-menopausal patients with estrogen receptor-positive tumors. Adjuvant anthracycline-based chemotherapy yielded a significant benefit for DFS by lowering the risk of distant metastases. After up to 10 years of follow-up, deferring radiotherapy after chemotherapy did not compromise local control.