OUTLINE: This is a randomized, double blind study. Patients are stratified by adjuvant chemotherapy regimen (cyclophosphamide, epirubicin, and fluorouracil vs cyclophosphamide, methotrexate, and fluorouracil vs cyclophosphamide and doxorubicin), hormone receptor status (ER and/or PR positive vs ER and PR negative), number of positive nodes (1-3 vs 4-9 vs 10 or more), and participating institution. Patients receive one of three regimens of adjuvant chemotherapy at the discretion of the investigator. Regimen A: Patients receive oral cyclophosphamide on days 1-14 and epirubicin IV and fluorouracil IV on days 1 and 8. Courses repeat every 28 days for a total of 6 courses. Following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Regimen B: Patients receive oral cyclophosphamide on days 1-14 or cyclophosphamide IV on day 1 and 8, methotrexate on days 1 and 8, and fluorouracil IV on days 1 and 8. Courses repeat every 28 days for a total of 6 courses. Concurrent with or following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Regimen C: Patients receive doxorubicin IV and cyclophosphamide IV every 21 days for a total of 4 courses. Following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Patients are then randomized to receive either oral tamoxifen or a placebo once daily for 5 years, beginning within 6 weeks of completion of chemotherapy. Treatment continues in the absence of disease progression or unacceptable toxicity. Patients are followed for survival.