This clinical trial studies use of [F-18] 16 alpha-fluoroestradiol ([F-18] FES) positron emission tomography (PET)/computed tomography (CT) in measuring tumor hormone receptor expression in patients undergoing endocrine-targeted therapy for newly diagnosed breast cancer or breast cancer that has come back or spread to other places in the body. Comparing results of diagnostic procedures done before, during, and after hormone therapy may help measure a patient's response to treatment.