Breast Density, Hormone Levels, and Anticancer Drug Levels in Women With Invasive Breast Cancer Who Are Receiving Exemestane or Anastrozole

OBJECTIVES: Primary * Assess the change in percent breast density and dense area in response to aromatase inhibitor therapy from pretreatment to 1 year, 1 year to 2 years, and pretreatment to 2 years in women with invasive breast cancer. * Determine the changes in percent breast density and dense area in response to aromatase inhibitor therapy from pretreatment to 1 year and correlate the changes with changes in plasma hormones (e.g., estrone, estrone-sulfate, estradiol, and sex hormone binding globulin) and drug levels (anastrozole or exemestane) over the same period in women with invasive breast cancer. * Determine the change over time in percent breast density and dense area (from pretreatment to the time period prior to local recurrence) in the contralateral breast in correlation to local recurrence of breast cancer. Secondary * Determine the change over time in percent breast density and dense area in the contralateral breast in correlation to the development of contralateral breast cancer. * Determine whether women with high pretreatment percent density (upper tertile) experience greater decreases in percent breast density at 1 and 2 years of aromatase inhibitor therapy than women with low pretreatment percent density (lower tertile). * Determine whether women with high pretreatment dense area (upper tertile) experience greater decreases in dense area at 1 and 2 years of aromatase inhibitor therapy than women with low pretreatment dense area (lower tertile). * Correlate haplotype tagged single nucleotide polymorphisms in genes in the aromatase pathway (identified thorough the Mayo Clinic and Indiana University Pharmacogenomics Research Network Projects) with changes in percent and area breast density, plasma hormone levels, and 1-year drug levels. OUTLINE: This is a multicenter, companion study. Patients complete a 10-minute questionnaire about factors that might affect changes in breast density at baseline and another questionnaire at 1 year and 2 years post registration. Blood samples are collected at baseline (before initiation of treatment ) and at 1 year post registration for hormone and drug level analysis. Mammograms taken prior to registration (within 12 months prior to enrollment) and at approximately 1 and 2 years post-registration to this study are retrieved and digitized for determination of percent breast density and dense area. PROJECTED ACCRUAL: A total of 550 patients will be accrued for this study.