OUTLINE: This is a randomized study. Patients are stratified according to stage of disease (stage II vs stage IIIA), lymph node status (at least 10 positive nodes vs less than 10 positive nodes), and hormone receptor status (estrogen receptor positive or progesterone receptor positive vs estrogen receptor negative or progesterone receptor negative). All patients initially receive mobilization chemotherapy with cyclophosphamide IV over 1-2 hours on day 1 and paclitaxel IV over 4 hours on day 2. Beginning on day 4, patients receive filgrastim (G-CSF) or sargramostim (GM-CSF) subcutaneously each day until the final day of leukapheresis. When blood counts recover, peripheral blood stem cells (PBSC) are harvested. Patients are randomized to 1 of 2 high dose chemotherapy regimens 28-45 days after the last dose of mobilization chemotherapy. Arm I: Patients receive oral busulfan every 6 hours on days -8 to -6, melphalan IV over 30-60 minutes on days -5 and -4, and thiotepa IV over 2 hours on days -3 and -2. PBSC are reinfused on day 0. Arm II: Patients receive cyclophosphamide, thiotepa, and carboplatin by continuous IV infusion over 24 hours on days -7, to -4. PBSC are reinfused on day 0. Beginning 4-6 weeks after the last dose of chemotherapy, patients in both arms receive local radiotherapy 5 days each week for 5 weeks. Patients also receive oral tamoxifen (or equivalent antiestrogen therapy) daily for 5 years if they are estrogen or progesterone receptor positive, postmenopausal, or age 50 and over and perimenopausal. Patients are followed every 3 months for 2 years and then every 6 months thereafter.