Study to Determine the Utility of FES-PET and FDG-PET in the Prediction of Response to Hormone Therapy in Women With Estrogen Positive Metastatic Breast Cancer

This study of hormone positive (estrogen receptor \[ER\]), metastatic invasive ductal breast cancer looks at functional scanning using positron emission tomography (PET) and patient response to hormone therapy. Functional scans allow investigators to see more than one metastatic location. The investigators will use an estrogen based agent (FES) to see the number of hormone positive metastases and compare that to positive lesions on routine glucose (FDG) based scanning. FES and FDG-PET results will be compared to give a FDG to FES ratio. The PET ratio will be calculated before hormone therapy and at relapse after treatment. The investigators will biopsy an accessible lesion that is FDG positive and FES negative and perform pathological testing for ER and PR positivity and compare it to the original primary tumor ER/PR. The investigators will test the lesion for tumor proliferation (using Ki-67) and aggressiveness using human epidermal growth factor receptor 2 (HER-2). Results will be compared to the primary tumor Ki-67 and HER-2 to determine concordance. The investigators will have pre-treatment results for FES and FDG-PET, will calculate the ratio, and will correlate it to the primary metastatic lesion and test for ER/PR, Ki-67, and HER-2, and subsequent response to therapy. The investigators will determine the FES-PET predictive value for determining appropriateness of hormone therapy for metastatic disease. With these results, the investigators plan to undertake future tumor biomarker/PET studies in metastatic breast cancer.