DISEASE CHARACTERISTICS:

• Histologically confirmed breast cancer confined to the breast and axillary nodes

  • No distant metastatic disease
  • Tumor detected in the internal mammary chain by sentinel node procedure allowed

• Must have undergone 1 of the following procedures for primary breast cancer within the past 12 weeks and have no known clinical residual locoregional disease:

  • Total mastectomy with or without adjuvant radiotherapy
  • Breast-conserving surgery (e.g., lumpectomy, quadrantectomy, or partial mastectomy with margins clear* of invasive cancer and ductal carcinoma in situ) followed by radiotherapy NOTE: *If all other margins are clear, a positive posterior (deep) margin is permitted, provided the excision was performed down to the pectoral fascia and all tumor has been removed OR a positive anterior (superficial; abutting skin) margin is allowed provided all tumor was removed

• Prior axillary lymph node dissection or negative axillary sentinel node biopsy required

  • Patients with microscopically positive axillary sentinel nodes allowed provided they were evaluated on a clinical trial evaluating microscopically positive lymph nodes

• No locally advanced, inoperable breast cancer, including any of the following characteristics:

  • Inflammatory breast cancer
  • Supraclavicular node involvement
  • Enlarged internal mammary nodes (unless pathologically negative)

• No prior ipsilateral or contralateral invasive breast cancer

  • Histologically diagnosed synchronous bilateral invasive breast cancer within the past 2 months allowed if the bilateral disease meets all other eligibility criteria

• Hormone receptor status:

  • Estrogen receptor and/or progesterone receptor positive in each tumor

    • At least 10% of tumor cells positive by immunohistochemistry

PATIENT CHARACTERISTICS:

Age

• Premenopausal

Sex

• Female

Menopausal status

• Premenopausal

  • Estradiol in the premenopausal range after surgery

Performance status

• Not specified

Life expectancy

• Not specified

Hematopoietic

• Not specified

Hepatic

• No systemic hepatic disease that would preclude prolonged follow-up

Renal

• No systemic renal disease that would preclude prolonged follow-up

Cardiovascular

• No prior deep venous thrombosis and/or embolism unless patient is medically suitable
• No systemic cardiovascular disease that would preclude prolonged follow-up

Pulmonary

• No systemic pulmonary disease that would preclude prolonged follow-up

Other

• Not pregnant or nursing
• Fertile patients must use effective nonhormonal contraception
• No other prior or concurrent invasive malignancy except adequately treated basal cell or squamous cell skin cancer, nonbreast carcinoma in situ without invasion, contralateral or ipsilateral carcinoma in situ of the breast

• No prior or concurrent nonbreast invasive malignancy within the past 5 years that is nonrecurrent including any of the following:

  • Stage I papillary thyroid cancer
  • Stage Ia carcinoma of the cervix
  • Stage Ia or b endometrioid endometrial cancer
  • Borderline or stage I ovarian cancer
• No other nonmalignant systemic disease that would preclude prolonged follow-up
• No history of noncompliance with medical regimens
• No psychiatric, addictive, or other disorder that would preclude study compliance or giving informed consent

PRIOR CONCURRENT THERAPY:

Biologic therapy

• Not specified

Chemotherapy

• No prior neoadjuvant or adjuvant chemotherapy

  • Neoadjuvant or adjuvant trastuzumab (Herceptin®) allowed

Endocrine therapy

• No prior neoadjuvant or adjuvant endocrine therapy after breast cancer diagnosis
• No prior tamoxifen or other selective estrogen-receptor modulator (e.g., raloxifene) within 1 year before the breast cancer diagnosis

• No other concurrent oral or transdermal hormonal therapy, including any of the following:

  • Estrogen
  • Progesterone
  • Androgens
  • Aromatase inhibitors
  • Hormone replacement therapy
  • Oral or other hormonal contraceptives, including implant and depot injections
  • Raloxifene or other selective estrogen-receptor modulators

Radiotherapy

• See Disease Characteristics
• No prior ovarian irradiation

Surgery

• See Disease Characteristics
• No prior bilateral oophorectomy

Other

• No other prior neoadjuvant therapy
• No other concurrent investigational agents
• No concurrent bisphosphonates unless bone density has been documented at least 1.5 standard deviations below the young adult normal mean or the patient is participating in a randomized clinical trial setting testing bisphosphonates in the adjuvant breast cancer setting