Letrozole or Tamoxifen in Treating Postmenopausal Women With Breast Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed resectable adenocarcinoma of the breast

  * pT1, pT2, pT3, or minimal dermal involvement on pathology only
  * pN0, pN1, pN2, or M0

    * Negative nodal status

      * At least 8 nodes are negative
    * Unknown nodal status

      * Less than 8 nodes examined and no pathological finding
    * Positive nodal status

      * Any positive finding independent of the number of nodes examined
  * Negative sentinel node or no prior nodal dissection allowed if all other criteria met
* Must have had total mastectomy, lumpectomy, or quadrantectomy

  * Should have prior chest wall radiotherapy after segmental mastectomy or histopathologic T4 dermal involvement
* Stage I, II, or IIIa allowed if the tumor is completely removed macroscopically and margins of the resected tumor are microscopically free of tumor
* Must undergo chest wall radiotherapy or second resection if microscopic disease at the mastectomy margins
* No bilateral disease except in situ disease, either ductal or lobular of the contralateral breast
* Postmenopausal

  * Regardless of prior hormonal replacement therapy (HRT) or hysterectomy:

    * Bilateral oophorectomy and any age
    * Radiologic castration and amenorrheic for at least 3 months and any age
    * Not postmenopausal at the start of adjuvant chemotherapy AND and completed at least 6 courses of prior cyclophosphamide, methotrexate, and fluorouracil (CMF) or at least 4 courses of prior anthracycline-cyclophosphamide continuation therapy and at least age 45 with follicle stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) postmenopausal levels
  * No prior HRT:

    * Prior hysterectomy and less than age 55 with FSH/LH/E2 postmenopausal levels
    * Prior hysterectomy and at least age 55
  * No prior HRT or hysterectomy:

    * Amenorrhea more than 1 year and less than age 50
    * Amenorrhea more than 6 months and at least age 50
  * Prior HRT regardless of hysterectomy:

    * At least 1 month since prior HRT and less than age 55 with FSH/LH/E2 postmenopausal levels
    * At least 1 month since prior HRT and at least age 55
  * FSH/LH/E2 postmenopausal levels and uncategorized
* No distant metastases, including bone scans showing hot spots unconfirmed as benign disease or skeletal pain of unknown cause
* At least 10% hormone receptor-positive tumor cells
* Hormone receptor status:

  * Estrogen receptor positive AND/OR
  * Progesterone receptor positive

PATIENT CHARACTERISTICS:

Age:

* 30 and over

Sex:

* Female

Menopausal status:

* Postmenopausal

Performance status:

* Not specified

Life expectancy:

* Not specified

Hematopoietic:

* WBC greater than 3,000/mm\^3
* Platelet count at least 100,000/mm\^3
* Hemoglobin greater than 10 g/dL

Hepatic:

* Bilirubin less than 3.0 mg/dL
* SGOT or SGPT less than 1.5 times upper limit of normal
* No hepatic disease that would preclude study

Renal:

* Creatinine less than 1.8 mg/dL
* No renal disease that would preclude study

Cardiovascular:

* No cardiovascular disease that would preclude study
* Prior deep vein thrombosis allowed if medically stable

Pulmonary:

* No lung embolism

Other:

* No other prior or concurrent malignancy within the past 5 years except adequately treated basal or squamous cell skin cancer or carcinoma in situ of the cervix
* No prior noncompliance to medical regimens
* No other nonmalignant systemic diseases that would preclude follow-up
* HIV negative

PRIOR CONCURRENT THERAPY:

Biologic therapy:

* Prior immunotherapy or biological response modifiers (e.g., interferon) allowed

Chemotherapy:

* See Disease Characteristics
* Prior adjuvant or neoadjuvant chemotherapy allowed
* Concurrent adjuvant chemotherapy allowed

Endocrine therapy:

* See Disease Characteristics
* Prior neoadjuvant hormonal therapy allowed (e.g., antiestrogens, progestins, or aromatase inhibitors) if no more than 4 months duration and no disease progression
* Prior corticosteroids allowed
* At least 4 weeks since prior HRT
* Prior adjuvant antiestrogen therapy allowed if less than 1 month duration and immediately after surgery, radiotherapy, and/or chemotherapy
* Prior antiestrogens for chemoprevention allowed if at least 18 months between completion of chemoprevention and diagnosis
* No other concurrent antiestrogens or aromatase inhibitors
* No concurrent raloxifene
* No concurrent systemic HRT with or without progestins of more than 3 months duration

Radiotherapy:

* See Disease Characteristics
* Concurrent radiotherapy allowed

Surgery:

* See Disease Characteristics

Other:

* At least 30 days since prior systemic investigational drugs
* At least 7 days since prior topical investigational drugs
* Concurrent bisphosphonates allowed