Inclusion Criteria

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

PATIENT CHARACTERISTICS: Age: Postmenopausal as defined below Sex: Female Menopausal
status: Postmenopausal as defined by: 55 years of age and over, and amenorrhea for greater
than 2 years OR Radiation menopause (at least 3 months previously) or surgical
oophorectomy OR Natural amenorrhea for at least 1 year at breast cancer diagnosis
Performance status: Not specified Life expectancy: Not specified Hematopoietic: WBC at
least 4,000/mm3 Hemoglobin normal Hepatic: SGOT no greater than 2.5 times upper limit of
normal (ULN) Renal: Creatinine no greater than 1.5 times ULN Cardiovascular: No
significant cardiac disorder Other: No significant skeletal or endocrine disorders No
clinical evidence of severe osteoporosis and/or history of osteoporotic fracture No other
prior malignancy except basal cell skin cancer or carcinoma in situ of the cervix No
psychiatric or addictive disorders

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease
Characteristics Prior or concurrent bisphosphonates allowed Adjuvant or neoadjuvant
chemotherapy for primary disease allowed Endocrine therapy: At least 4 weeks since prior
hormone replacement therapy (oral, topical, or vaginal) Prior low-dose progestins for
relief of menopausal symptoms (up to 6 months duration) allowed No concurrent progestins
No concurrent systemic corticosteroids for a prolonged period (i.e., greater than 2 weeks)
No concurrent selective estrogen receptor modulators Radiotherapy: See Disease
Characteristics Surgery: See Disease Characteristics Other: Prior participation and
completion of therapy on another clinical study of systemic therapy (e.g., comparison of
chemotherapy schedules) allowed No concurrent warfarin Concurrent treatment for other
diseases allowed only when clinically indicated