Inclusion Criteria

DISEASE CHARACTERISTICS:

- One of the following histologically proven diagnoses:

- Primary invasive adenocarcinoma of the unilateral or bilateral breast

- Stage I, IIA, or IIB (T1-3, N0-1, M0)

- No recurrent invasive breast cancer

- Ductal carcinoma in situ (DCIS)

- Lobular carcinoma in situ (LCIS) with microinvasion

- Paget's disease of the nipple

- No sarcoma, lymphoma, or apocrine, adenocystic, or squamous cell cancer of the breast

- Currently free of breast cancer (no evidence of disease)

- No evidence of distant disease on chest x-ray or chest CT scan and mammogram of
the opposite breast within the past year

- Prior definitive local treatment of primary lesion (mastectomy or breast-sparing
procedure with radiotherapy) and either axillary node or sentinel node biopsy

- Surgical margins clear of both infiltrating carcinoma (any type) and DCIS

- No gross or microscopically positive margins except:

- Invasive cancer or DCIS at the focal margin treated with definitive
radiotherapy

- Gross or LCIS at the final margin

- Biopsy requirement waived for DCIS or LCIS with minimal microinvasion

- Patients with breast-sparing procedure must have received or be planning to receive
radiotherapy at start of tamoxifen treatment

- No endometrial simple or cystic hyperplasia, proliferative changes, complex
(adenomatous) or atypical hyperplasia, or carcinoma

- Patients must be planning one of the following:

- Starting adjuvant tamoxifen for five years OR

- Started tamoxifen within 28 days prior to study and planning to receive adjuvant
tamoxifen for five years

- Hormone receptor status:

- Candidate for adjuvant tamoxifen therapy

PATIENT CHARACTERISTICS:

Age:

- Adult

Sex:

- Female

Menopausal status:

- Postmenopausal defined as:

- At least 1 year since last menstrual period

- At least 2 months since bilateral oophorectomy prior to breast cancer diagnosis

- 4-12 months since last menstrual period and FSH elevated to postmenopausal range

- Postmenopausal estrogen therapy and 55 years of age or older

Performance status:

- Not specified

Life expectancy:

- Not specified

Hematopoietic:

- Not specified

Hepatic:

- Not specified

Renal:

- Not specified

Other:

- Fertile patients must use effective contraception during and for at least 2 months
after study

- No other malignancy within the past 5 years except adequately treated basal cell or
squamous cell skin cancer, carcinoma in situ of the cervix, or stage I or II cancer
currently in complete remission

- No concurrent nonmalignant-related illness that would preclude study

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- Not specified

Chemotherapy:

- Adjuvant chemotherapy allowed

- No concurrent chemotherapy

Endocrine therapy:

- See Disease Characteristics

- No prior hormonal treatment for breast cancer (except tamoxifen)

- No concurrent postmenopausal estrogen therapy

Radiotherapy:

- See Disease Characteristics

Surgery:

- See Disease Characteristics

- No prior or concurrent hysterectomy

Other:

- No prior or current participation in an adjuvant intergroup trial