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