OUTLINE: This is a randomized study, multicenter study. Patients are stratified according to nodal status (positive vs negative or unknown) and hospital region. Patients undergo surgical resection with or without local radiotherapy, as appropriate. Radiotherapy begins within 8 weeks of surgery for patients randomized to arm I and within 4 weeks after completion of chemotherapy for patients randomized to arm II. Patients are randomized to 1 of 2 treatment arms, preferably within 2 weeks after surgery. Arm I: Beginning within 4 weeks after surgery, patients receive oral tamoxifen daily. Treatment continues for 5 years. Arm II: Beginning within 4 weeks after surgery, patients receive tamoxifen as in arm I and cyclophosphamide IV, methotrexate IV, and fluorouracil IV on day 1 (CMF). Chemotherapy continues every 3 weeks for 6 courses. Patients are followed every 6 months for 5 years and then annually thereafter.