RATIONALE: Estrogen can cause the growth of breast cancer cells. Hormone therapy using tamoxifen may fight breast cancer by blocking use of estrogen by the tumor cells. Anastrozole, letrozole, and exemestane may fight breast cancer by lowering the amount of estrogen the body makes. It is not yet known whether giving tamoxifen followed by anastrozole, letrozole, or exemestane is more effective than giving anastrozole, letrozole, or exemestane alone in treating breast cancer.