Study of Anastrozole, Letrozole, or Exemestane With or Without Tamoxifen in Treating Postmenopausal Women With Hormone-Responsive Breast Cancer That Has Been Completely Removed By Surgery

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. PURPOSE: This randomized phase III trial is studying giving tamoxifen followed by either anastrozole, letrozole, or exemestane to see how well it works compared to anastrozole, letrozole, or exemestane alone in treating postmenopausal women with hormone-responsive invasive breast cancer that has been completely removed by surgery.