PET Scans in Assessing Response To Treatment in Patients Receiving Hormone Therapy or Trastuzumab for Breast Cancer

OBJECTIVES: * Correlate the percent change in fludeoxyglucose F 18 (FDG)-positron emission tomography (PET) standardized uptake value (SUV) and percent change in cell proliferation (as assessed by tumor biopsy) during hormonal therapy with tumor response in patients with hormone receptor-positive (estrogen receptor or progesterone receptor) breast cancer. * Correlate the percent change in FDG-PET SUV and percent change in cell proliferation (as assessed by tumor biopsy) during treatment with trastuzumab (Herceptin®) with tumor response in patients with HER-2/neu-positive breast cancer. * Compare the association between two-week changes in cell proliferation rate (as measured by FDG-PET and biopsy) in patients treated with an aromatase inhibitor or trastuzumab. OUTLINE: Patients are assigned to 1 of 2 groups according to therapy. * Group 1 (patients receiving hormonal therapy): Patients undergo fludeoxyglucose F 18-positron emission tomography (FDG-PET) scan and may also undergo 16α-fluoroestradiol F 18 (FES)-PET scan at baseline (prior to beginning therapy) and FDG-PET scan 2 weeks after beginning therapy. Blood samples are collected at baseline and at 3 and 6 months after beginning aromatase inhibitor therapy. The blood samples are examined for hormone levels, including estradiol, estrone, testosterone, follicle-stimulating hormone, and sex hormone-binding globulin. * Group 2 (patients receiving HER-2/neu targeted therapy): Patients undergo biopsy and FDG-PET scan at baseline (prior to beginning therapy) and FDG-PET scan 1-2 weeks after beginning therapy. Some patients undergo a core-needle biopsy 2 weeks after beginning therapy. Biopsies are assessed for the following markers: proliferative rate (Ki67), estrogen receptor, progesterone receptor, HER-2/neu, epidermal growth factor receptor, androgen receptor, and topoisomerase II. After completion of study therapy, patients are followed periodically for 6 months. PROJECTED ACCRUAL: A total of 40 patients will be accrued for this study.