Letrozole in Treating Breast Cancer in Postmenopausal Women With Stage I, II, or III Breast Cancer Previously Treated With Tamoxifen (GIM4)

OBJECTIVES: Primary * To compare the disease-free survival of previously treated, post-menopausal women with early-stage breast cancer treated with standard- (2-3 years of tamoxifen followed by 2-3 years of letrozole) versus long-treatment (2-3 years of tamoxifen followed by 5 years of letrozole) adjuvant letrozole. Secondary * To compare the overall survival of these patients. * To compare the safety of these patients. OUTLINE: Patients are randomized to 1 or 2 treatment arms. * Arm I (standard treatment): Patients previously treated with tamoxifen for 2 years receive letrozole for an additional 3 years; patients previously treated with tamoxifen for 3 years receive letrozole for an additional 2 years; and patients previously treated with tamoxifen for 2-3 years receive letrozole , so the total duration of the endocrine treatment (i.e., tamoxifen followed by letrozole) is 5 years. * Arm II (long treatment): Patients receive letrozole for an additional 5 years regardless of the duration of the previous tamoxifen treatment.