Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed invasive breast cancer

- pT1-3; pNX, pN0-2 or pN3*; M0

- Neoadjuvant patients are eligible no earlier than 3 weeks or later than 3 months
after excisional surgery, provided both the clinical-diagnostic staging of
cancer and postsurgical resection-pathologic staging of cancer meet the
requirements for primary tumor, regional lymph nodes, and distant metastasis
classification NOTE: *Only when the sole basis for this classification is the
presence of 10 or more involved axillary lymph nodes

- Completely resected disease

- Primary surgery performed at least 3 weeks but no more than 3 months before
study entry (if no chemotherapy was given)

- Primary surgery is defined as the last surgery at which histologic evidence
of invasive or in situ disease was present in the pathology specimen

- Patients with positive sentinel lymph node biopsy are eligible provided they
have had a subsequent axillary lymph node dissection

- No metachronous breast cancer

- Bilateral mammogram within the past 12 months unless initial surgery was a total
mastectomy, in which case only a mammogram of the remaining breast is required

- No metastases confirmed by 1 of the following methods:

- Bone scan* (required only if alkaline phosphatase is at least 2 times normal
and/or there are symptoms of metastatic disease)

- Abdominal ultrasound or CT scan (required only if AST/ALT or alkaline
phosphatase is at least 2 times normal, unless the elevation is in the bone
fraction)

- Chest x-ray NOTE: *Confirmatory x-ray, CT scan, or MRI required if the bone scan
results are questionable

- No locally recurrent disease

- No prior or concurrent carcinoma in situ of the contralateral breast treated with
partial mastectomy and/or hormonal therapy

- Patients with prior or concurrent carcinoma in situ of the ipsilateral breast
are eligible provided the tumor was completely excised AND they have not
received prior hormonal therapy

- Hormone receptor status:

- Estrogen receptor- and/or progesterone receptor-positive by immunohistochemistry
or tumor receptor content ≥ 10 fmol/mg protein

PATIENT CHARACTERISTICS:

Age

- Postmenopausal

Sex

- Female

Menopausal status

- Postmenopausal prior to chemotherapy, defined as 1 of the following:

- Over 60 years of age

- Age 45-59 with spontaneous cessation of menses for more than 1 year prior to
study entry

- Age 45-59 with menses ceasing (secondary to hysterectomy or spontaneously)
within the past year AND a follicle-stimulating hormone (FSH) level prior to
study entry in the postmenopausal range*

- Age 45-59, previously on hormone replacement therapy (HRT) and have discontinued
HRT upon diagnosis of this malignancy AND has an FSH level prior to study entry
in the postmenopausal range*

- Has undergone bilateral oophorectomy NOTE: *By institutional standards OR > 34.4
IU/L if institutional range is not available)

Performance status

- ECOG 0-2

Life expectancy

- At least 5 years

Hematopoietic

- WBC at least 3,000/mm^3 OR

- Granulocyte count at least 1,500/mm^3 AND

- Platelet count at least 100,000/mm^3

Hepatic

- See Disease Characteristics

- AST and/or ALT less than 2 times upper limit of normal (ULN)*

- Alkaline phosphatase less than 2 times ULN* NOTE: *Unless imaging examinations have
ruled out metastatic disease

Renal

- Not specified

Other

- Able to swallow study medication and have adequate unassisted oral intake in order to
maintain reasonable nutrition status

- No other non-breast malignancy within the past 5 years except adequately treated
nonmelanoma skin cancer, curatively treated carcinoma in situ of the cervix, or other
curatively treated solid tumors with no evidence of disease for at least 5 years

- No other concurrent medical or psychiatric condition that would preclude study
participation and/or interfere with results

PRIOR CONCURRENT THERAPY:

Biologic therapy

- Prior and concurrent trastuzumab (Herceptin®) allowed

Chemotherapy

- See Disease Characteristics

- At least 3 weeks but no more than 3 months since prior chemotherapy

- Prior adjuvant chemotherapy allowed

Endocrine therapy

- See Disease Characteristics

- No prior aromatase inhibitor

- No prior tamoxifen or other selective estrogen receptor modulators (SERMs) except
raloxifene

- At least 3 weeks since prior raloxifene

- At least 3 weeks since prior and no concurrent over-the-counter products or
supplements considered to have an estrogenic effect, including any of the following:

- Ginseng

- Ginkgo biloba

- Black cohosh

- Dong quai

- Fortified soy supplements (e.g., phytoestrogen preparations)

- At least 3 weeks since other prior hormonal therapy or steroids considered to have an
estrogenic effect

- No concurrent estrogens, progesterones, androgens, or SERMs

- Concurrent intermittent vaginal estrogens (e.g., vagifem, estrogen vaginal
cream, testosterone, estradiol vaginal gel, or Estring) allowed if other local
measures for intractable vaginal atrophy are insufficient

- No other concurrent therapy that would have an estrogenic effect, including endocrine
therapy, hormonal therapy, or steroid therapy

Radiotherapy

- See Disease Characteristics

- Prior adjuvant radiotherapy allowed

- Concurrent radiotherapy allowed

Surgery

- See Disease Characteristics