DISEASE CHARACTERISTICS: At diagnosis: Histologically confirmed unilateral adenocarcinoma of the breast that was considered operable Must have had adequate therapy for primary disease including chemotherapy/ovarian ablation if appropriate and local postoperative radiotherapy if the patient received conservative (breast preserving) surgery Must have remained disease-free after therapy for primary disease Must have been receiving tamoxifen for minimum of 2 years and maximum of 3 years 1 month with no more than 1 month break at any one time No inflammatory breast cancer, histologically positive supraclavicular nodes, or ulceration/infiltration or skin metastases No evidence of local relapse or distant metastasis (on chest x-ray, scintigraphic bone scanning and liver ultrasonography/CT scanning) at any time Hormone receptor status: Estrogen receptor positive or unknown