OUTLINE: This is a randomized, multicenter, open label study. Patients are stratified by study center and number of positive axillary lymph nodes at surgery. Patients are randomized to receive conventional or high dose adjuvant chemotherapy. Arm I: Patients receive conventional chemotherapy consisting of cyclophosphamide, methotrexate, and fluorouracil IV administered once every 3 weeks for 8 courses. Arm II: Patients receive high dose chemotherapy. Cyclophosphamide IV is administered on day 1. Patients undergo peripheral blood progenitor cell (PBPC) collection, then receive cyclophosphamide and thiotepa IV for 4 days, 13-28 days after PBPC collection. Peripheral blood progenitor cells are then reinfused. Patients undergo radiotherapy during or after chemotherapy and receive oral tamoxifen for 5 years, beginning at the same time as radiotherapy. Estrogen receptor negative patients may receive tamoxifen at the discretion of the treating physician. Quality of life is assessed before chemotherapy, then at 6, 12, and 24 months. Patients are followed at 12, 18, and 24 months, then annually for 5 years or until death.