Letrozole in Treating Postmenopausal Women Who Have Received Hormone Therapy for Hormone Receptor-Positive Breast Cancer

RATIONALE: Estrogen can cause the growth of breast cancer cells. Hormone therapy using letrozole may fight breast cancer by lowering the amount of estrogen the body makes. It is not yet known whether letrozole is more effective than a placebo in treating patients with hormone receptor-positive breast cancer. PURPOSE: This randomized phase III trial is studying letrozole to see how well it works compared with a placebo in treating postmenopausal women who have received hormone therapy for hormone receptor-positive breast cancer.