Exemestane in Treating Postmenopausal Women With Resected Stage I, Stage II, or Stage IIIA Breast Cancer Who Have Completed 5 Years of Tamoxifen

DISEASE CHARACTERISTICS:

Histologically confirmed invasive adenocarcinoma of the breast at time of original diagnosis

Tumor confined to the breast and ipsilateral axilla on clinical exam (T1-3, N0-1, M0) (stage I-IIIA)
No ipsilateral lymph nodes clinically fixed to one another or to other structures (N2 disease) at time of original diagnosis

Prior surgical resection, including 1 of the following:

Total mastectomy and axillary dissection (modified radical mastectomy) OR

Lumpectomy and axillary dissection

Prior post-lumpectomy breast radiotherapy required

Prior sentinel node biopsy allowed with the exception of the following:

If any sentinel node is histologically positive by hematoxylin and eosin (H & E) OR histologically suspicious on H & E and confirmed positive by immunohistochemistry then the patient must have a complete axillary dissection
Previously resected margins must be clear of invasive tumor and ductal carcinoma in situ
Currently disease free

Previously treated with tamoxifen for 57-66 months

Completed tamoxifen within the past 180 days
No bilateral malignancy or mass in the opposite breast suspicious for malignancy unless biopsy proven negative
No local, regional, or distant recurrence of disease or second primary breast malignancy (including contralateral breast cancer)

No advanced disease at time of original diagnosis (e.g., ulceration, erythema, infiltration of the skin or underlying chest wall [complete fixation], peau d'orange, or skin edema of any magnitude)

Tethering or dimpling of the skin or nipple inversion allowed
Current skeletal pain allowed if a bone scan and/or radiologic exam is negative for metastatic disease

Hormone receptor status:

Primary tumor estrogen receptor (ER) positive AND/OR
Progesterone receptor positive
Borderline ER positive tumors allowed if previously treated with tamoxifen

PATIENT CHARACTERISTICS:

Age:

Postmenopausal

Sex:

Female

Menopausal status:

Postmenopausal, defined as 1 of the following:

Prior bilateral oophorectomy
Absence of spontaneous menstrual cycle for more than 1 year
Follicle-stimulating hormone within the postmenopausal range if under 55 and had a prior hysterectomy without a bilateral oophorectomy

Performance status:

Not specified

Life expectancy:

At least 10 years

Hematopoietic:

Absolute granulocyte count at least 1,500/mm^3
Platelet count at least 100,000/mm^3
Hemoglobin normal

Hepatic:

Bilirubin less than 2 times upper limit of normal (ULN)
SGOT or SGPT no greater than 2.5 times ULN
Alkaline phosphatase less than 2 times ULN
No systemic hepatic disease that would preclude study participation

Renal:

Creatinine no greater than 1.5 times ULN
No systemic renal disease that would preclude study participation

Cardiovascular:

No systemic cardiovascular disease that would preclude study participation

Other:

No other malignancy within the past 5 years except effectively treated squamous cell or basal cell skin cancer, surgically treated carcinoma in situ of the cervix, or surgically treated lobular carcinoma in situ of the ipsilateral or contralateral breast
No nonmalignant systemic disease that would preclude study participation
No psychiatric or addictive disorder that would preclude informed consent
Not pregnant

PRIOR CONCURRENT THERAPY:

Biologic therapy:

Not specified

Chemotherapy:

Prior adjuvant chemotherapy allowed if administered concurrently with or prior to tamoxifen

Endocrine therapy:

See Disease Characteristics

No concurrent estrogen, progesterone, clomiphene, testosterone, gonadotropin-releasing hormone, oral contraceptives, selective estrogen-receptor modulators, or dehydroepiandrosterone (DHEA)

Estring or estrogen vaginal cream at 0.3 mg or 1/8 of an applicator applied vaginally 3 times a week allowed
No other concurrent systemic hormonal therapy (e.g., tamoxifen or raloxifene)

Radiotherapy:

See Disease Characteristics
Prior post-mastectomy loco-regional radiotherapy or post-lumpectomy regional radiotherapy allowed

Surgery:

See Disease Characteristics

Other:

Prior participation in other adjuvant NSABP study allowed if study was reported in peer-review publication or tamoxifen was not a study drug
Concurrent bisphosphonates or calcitonin for prevention or treatment of osteoporosis allowed
Concurrent statins (simvastatin, pravastatin, fluvastatin, atorvastatin, or lovastatin) or other drugs to control lipid levels allowed