RATIONALE: Estrogen can cause the growth of breast cancer cells. Hormone therapy using tamoxifen may fight breast cancer by blocking the use of estrogen by the tumor cells. Drugs used in chemotherapy, such as doxorubicin, cyclophosphamide, and fluorouracil, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. It is not yet known whether giving tamoxifen alone is more effective in treating breast cancer than giving tamoxifen together with chemotherapy or after chemotherapy.