Changes in Breast Density and Blood Hormone Levels in Postmenopausal Women Receiving Anastrozole or Exemestane for Breast Cancer

DISEASE CHARACTERISTICS: Inclusion criteria: * Must have histologically confirmed invasive breast cancer, as defined by the following TNM staging criteria: * pT1, pT2, or pT3 * pNx, pN0, pN1, pN2, or pN3\* * Patients with positive sentinel node biopsies (pN1) must have subsequent axillary dissection to be eligible * Patients with negative sentinel node biopsies (pN0) do not require axillary surgery for study eligibility * M0, according to the following radiologic studies: * Bone scan (required only if alkaline phosphatase is \> 2 x institutional upper limit of normal \[ULN\] and/or there are symptoms of metastatic disease) * A confirmatory x-ray or other imaging study, such as CT scan or MRI, is required if the results from the bone scan are questionable * Abdominal ultrasound or CT scan of the abdomen (required only if AST/ALT or alkaline phosphatase is \> 2 x ULN unless the elevation is in the bone fraction) * Chest x-ray NOTE: \*Only when the sole basis for this classification is the presence of 10 or more involved axillary nodes * Completely resected disease * Surgical margins must be clear of invasive carcinoma and ductal carcinoma in situ or lobular carcinoma in situ * Must have one intact, noncancerous breast with no history of previous breast surgery in that breast (other than a breast biopsy) * Mammogram of the intact, noncancerous breast required ≤ 6 months prior to study registration (both a craniocaudal \[top down\] and mediolateral oblique view \[side view\] must be available) * Must be registered on this study ≥ 3 weeks but ≤ 3 months after completion of chemotherapy OR primary surgery\* * Adjuvant chemotherapy and radiation therapy as prescribed by the local institution is allowed provided patient is registered on this study and hormonal treatment is begun as soon as patient has sufficiently recovered from chemotherapy NOTE: \*Primary surgery is defined as the last surgical procedure to remove invasive or in situ disease * Planning to receive anastrozole or exemestane for ≥ 1 year for treatment of breast cancer * Hormone receptor status: * Estrogen receptor- and/or progesterone receptor-positive (defined as a tumor receptor content of \> 10 fmol/mg protein OR receptor-positive by immunohistochemistry \[ERICA or PgRICA\]) PATIENT CHARACTERISTICS: Inclusion criteria: * Female * Postmenopausal, defined by one of the following: * Age \> 60 years * Age 45-59 years with spontaneous cessation of menses \> 12 months prior to chemotherapy (if no chemotherapy was given, then prior to study registration) * Age 45-59 years with cessation of menses for a duration of \< 12 months or secondary to hysterectomy AND an FSH level in the postmenopausal range (or ≥ 34.4 IU/L, if institutional range is not available) prior to chemotherapy (if no chemotherapy was given, then prior to study registration) * Age 45-59 years with an FSH level in the postmenopausal range according to institutional laboratory standards (or \> 34.4 IU/L, if the institutional range is not available) prior to chemotherapy (if no chemotherapy was given, then prior to study registration) * Bilateral oophorectomy * ECOG performance status 0, 1, or 2 * Life expectancy ≥ 5 years Exclusion criteria: * History of other (non-breast) malignancies, except adequately treated nonmelanoma skin cancer, curatively treated in situ cancer of the cervix, or other curatively treated solid tumors with no evidence of disease for \> 5 years * Any co-existing medical or psychiatric condition that is likely to interfere with study procedures and/or results PRIOR CONCURRENT THERAPY: Inclusion criteria: * See Disease Characteristics Exclusion criteria: * Hormone replacement therapy, oral contraceptives, tamoxifen, raloxifene, other selective estrogen-receptor modulators, or gonadotropin releasing-hormone analogues ≤ 6 months prior to the pre-registration mammogram * Prior treatment with an aromatase inhibitor (e.g., anastrozole, exemestane, letrozole) * Planned surgery (other than core needle biopsy) to intact non-cancerous breast (e.g., preventive/prophylactic mastectomy)