Letrozole After Tamoxifen in Treating Women With Breast Cancer

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