Inclusion Criteria

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