DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed primary invasive breast carcinoma resected at time of original diagnosis

  • No ductal carcinoma in situ
• Axillary lymph node negative, positive, or unknown
• No evidence of metastases
• No localized or distant breast cancer recurrence
• Not registered on protocol NCCTG-893052, any other IBCSG protocol, or protocol SWOG-S9623

• Hormone receptor status:

  • Estrogen or progesterone receptor positive as defined by tumor receptor content at least 10 fmol/mg protein or receptor positive by ERICA or PgRICA
  • Unknown status allowed if effort to determine status has been made by immunocytochemistry
• No contralateral breast cancer

PATIENT CHARACTERISTICS:

Age:

• Postmenopausal

Sex:

• Female

Menopausal status:

• Postmenopausal defined by one of the following:

  • Age 50 or over at start of adjuvant tamoxifen
  • Under age 50 and considered postmenopausal by treating physician at start of adjuvant tamoxifen
  • Under age 50 at start of adjuvant tamoxifen and had bilateral oophorectomy (surgical or radiation)
  • Under age 50 and premenopausal at start of adjuvant tamoxifen, but became amenorrheic during tamoxifen and remained amenorrheic for at least 1 year
  • Considered postmenopausal by physician with LH/FSH levels under the treatment center's postmenopausal limits

Performance status:

• ECOG 0-2

Life expectancy:

• At least 5 years

Hematopoietic:

• WBC ≥ 3,000/mm^3 OR
• Granulocyte count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3

Hepatic:

• AST and/or ALT < 2 times upper limit of normal (ULN) (unless imaging examinations have ruled out metastatic disease)
• Alkaline phosphatase < 2 times ULN (unless imaging examinations have ruled out metastatic disease)

Renal:

• Not specified

Other:

• No concurrent medical or psychiatric condition that would preclude study participation
• No other malignancy within the past 5 years except adequately treated superficial squamous cell or basal cell skin cancer or carcinoma in situ of the cervix
• Able to swallow study drug
• Adequate oral intake

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• Prior adjuvant chemotherapy allowed
• No concurrent chemotherapy

Endocrine therapy:

• Completed at least 4.5 but no more than 6 years of adjuvant tamoxifen after resection
• Completed at least 4.5-6 years of adjuvant aromatase inhibitor as initial therapy or after tamoxifen
• No more than 3 months since prior adjuvant tamoxifen
• No concurrent hormone replacement therapy (e.g., megestrol)
• No concurrent selective estrogen-receptor modulators (e.g., raloxifene or idoxifene)
• Concurrent intermittent vaginal estrogens (e.g., Estring) allowed if other local measures for intractable vaginal atrophy are insufficient
• No other concurrent aromatase inhibitors
• No more than 2 years since prior aromatase inhibitor therapy (re-randomization)

Radiotherapy:

• Prior radiotherapy allowed

Surgery:

• See Disease Characteristics

Other:

• At least 1 month since prior investigational drugs
• Prior treatment on a clinical trial for breast cancer allowed if permission has been obtained from the sponsors of the original study for their patient to participate on MA.17/JMA.17/BIG-97-01
• No prior placebo on core protocol
• No concurrent anticancer therapy
• Concurrent thyroid medication, calcium, vitamin D, and bisphosphonates allowed