Anastrozole in Treating Postmenopausal Women With DCIS or Stage I-III Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed breast cancer meeting 1 of the following criteria: * Ductal carcinoma in situ (DCIS) * Invasive carcinoma * Stage I-III disease * Must have undergone breast cancer surgery within the past 6 months, including any of the following: * Mastectomy or lumpectomy with or without radiation * Sentinel node and/or axillary node dissection * Re-excision of lumpectomy margins * Intact contralateral breast * No prior radiation therapy or mastectomy * Prior biopsies allowed * Hormone receptor status: * Estrogen and/or progesterone receptor-positive tumor by immunohistochemical staining PATIENT CHARACTERISTICS: Sex * Female Menopausal status * Postmenopausal, defined as 1 of the following: * At least 60 years of age * Less than 60 years of age and amenorrheic ≥ 12 months prior to study entry * Less than 60 years of age, amenorrheic for \< 12 months prior to day 1, and luteinizing hormone (LH) and follicle stimulating hormone (FSH) values within postmenopausal range * Less than 60 years of age, without a uterus, and LH and FSH values within postmenopausal range * Underwent prior bilateral oophorectomy * Underwent prior radiation castration AND amenorrheic for ≥ 6 months Performance status * ECOG 0-2 Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified PRIOR CONCURRENT THERAPY: Chemotherapy * No prior or concurrent adjuvant chemotherapy for breast cancer Endocrine therapy * No prior aromatase inhibitor * At least 6 weeks since prior and no concurrent tamoxifen * At least 6 weeks since prior and no concurrent hormone replacement therapy * Concurrent low-dose, local vaginal estrogen in the form of either a conjugated estrogen ring or other similar product (e.g., Estring® or Vagifem®) allowed * At least 6 weeks since prior and no other concurrent selective estrogen receptor modulators (e.g., raloxifene) Radiotherapy * See Disease Characteristics Surgery * See Disease Characteristics * No contralateral breast implant Other * Concurrent bisphosphonates allowed at the discretion of the treating oncologist * No concurrent consumption of soy supplements * Concurrent routine dietary consumption of soy-containing foods allowed * No other concurrent investigational or commercial drugs or therapies for the treatment of DCIS or invasive breast cancer