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