OUTLINE:~Patients undergo F-18 FES PET/CT scan at baseline. Patients also undergo F-18 FES PET/CT and FDG PET/CT between 1-12 weeks after starting therapy, and then 1-12 weeks after the second FES PET/CT scan. Repeat FDG PET may be omitted in patients on selective estrogen receptor degrader.~After completion of study, patients are followed up for up to 20 years.
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.