Study of Anastrozole, Letrozole, or Exemestane With or Without Tamoxifen in Treating Postmenopausal Women With Hormone-Responsive Breast Cancer That Has Been Completely Removed By Surgery

DISEASE CHARACTERISTICS:

* Histologically confirmed invasive breast cancer completely removed by surgery

  * Any T, any N
  * No recurrent or metastatic disease
* Estrogen or progesterone receptor-positive disease in primary tumor, as defined by 1 of the following:

  * At least 10% of tumor cells positive by immunohistochemistry
  * At least 10 fmol/mg cytosol protein by ligand binding assay
* Patients with HER-2/neu positive tumors are eligible provided they receive trastuzumab (Herceptin®) according to the registered schedule

PATIENT CHARACTERISTICS:

* Female
* Postmenopausal, defined by ≥ 1 of the following:

  * Age ≥ 60 years
  * Age 45-59 and satisfying 1 or more of the following criteria:

    * Amenorrhea for ≥ 12 months AND intact uterus
    * Amenorrhea (secondary to hysterectomy, hormone replacement therapy (HRT), or chemotherapy) for \< 12 months AND follicle-stimulating hormone within the postmenopausal range
  * Underwent prior bilateral oophorectomy at any age \>18 years
* No concurrent illness that contraindicates adjuvant endocrine treatment
* No other invasive breast cancer or invasive malignancy within the past 10 years, except adequately cone-biopsied squamous cell or basal cell skin cancer or carcinoma in situ of the cervix
* No concurrent disease that would place the patient at unusual risk

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* Adjuvant or neoadjuvant chemotherapy must be completed prior to study entry
* At least 1 month since prior and no concurrent HRT
* More than 30 days since prior systemic investigational drugs
* No prior tamoxifen as part of any breast cancer prevention study
* Prior or concurrent locoregional radiotherapy allowed
* No other concurrent experimental drugs
* No concurrent bisphosphonates, unless indicated as treatment for osteoporosis