OUTLINE: This is a randomized study. Patients are stratified by type of primary therapy and participating institution. Therapy must begin within 6 weeks of surgery. Patients in the first group receive doxorubicin (or epirubicin) and cyclophosphamide every 28 days for a total of 4 cycles and oral tamoxifen daily for 5 years, beginning day 1 of chemotherapy. Patients in the second group receive the same chemotherapy with oral tamoxifen initiated on day 8 of the fourth chemotherapy cycle and continued for 5 years. Patients in the third group receive oral tamoxifen daily for 5 years. Patients in the fourth group are treated the same as the first group, only tamoxifen is replaced by toremifene. Patients in the fifth group are treated the same as the second group, only tamoxifen is replaced by toremifene. Patients in the sixth group receive oral toremifene daily for 5 years. The timing of optional radiotherapy for patients with less than total mastectomy in each group is based on institutional policy; radiotherapy is administered for 5-6 weeks to the remaining breast tissue, chest wall, and lung. Patients are followed every 3 months for 1 year, every 6 months for 2 years, and yearly thereafter.