OBJECTIVES: I. Compare, in terms of disease-free survival and overall survival, the sequential administration of exemestane with administration of further tamoxifen until 5 years of therapy is achieved in postmenopausal women with operable breast cancer who have already received 2-3 years of adjuvant tamoxifen. II. Compare the regimens in terms of the incidence of contralateral breast cancer and long term tolerability of the regimens in these patients. III. Determine the tolerability of each regimen in terms of endometrial status, bone metabolism, lipid profile, and coagulation profile in these patients. IV. Assess quality of life in these patients treated with these regimens.