Letrozole in Breast Cancer Who Have Received 5 Years of Aromatase Inhibitor Therapy

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 in women with breast cancer who have already received 5 years of aromatase inhibitor therapy. PURPOSE: This randomized phase III trial is studying letrozole to see how well it works compared with a placebo in treating women with primary breast cancer who have received 5 years of aromatase inhibitor therapy.