Letrozole, Anastrozole, Exemestane, or Tamoxifen Citrate in Treating Postmenopausal Women With Breast Cancer

RATIONALE: Estrogen can cause the growth of breast cancer cells. Aromatase inhibitors, such as letrozole, anastrozole, and exemestane, may fight breast cancer by lowering the amount of estrogen the body makes. Hormone therapy, using tamoxifen citrate, may fight breast cancer by blocking the use of estrogen by the tumor cells. It is not yet known whether aromatase inhibitors or tamoxifen citrate have less effect on memory in patients receiving treatment for breast cancer. PURPOSE: This randomized phase III trial is studying letrozole, anastrozole, or exemestane to see how they effect memory compared with tamoxifen citrate in treating postmenopausal women with breast cancer.