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