The Value of 18F-FES-PET/CT in Predicting Fulvestrant Efficacy in Breast Cancer

This study is an open, multi-center and prospective clinical study, It is the first time investigators are examining this imaging agent in Chinese patients with breast cancer. The Chinese FDA has approved 18F-FES as an investigational tracer in a selective few research studies. The Chinese FDA has not approved this tracer for any use outside of research. In this research study, the investigators are investigating the use of a PET tracer called 18F-FES in patients with breast cancer. The purpose is to take images that can measure the amount of a protein called Estrogen Receptor, or 'ER' in breast tumors. The expression level of ER is tightly correlated with the Fulvestrant efficacy in patients with breast cancer. The investigators will take the pictures of the participant's residual tumor lesions using a PET/CT scanner with 18F-FES used as the tracer before and after the first cycle of Fulvestrant treatment. The investigators are trying to clarify the relationship between the clinical Fulvestrant efficacy and the amount change of 18F-FES uptake by breast tumor around the first cycle of Fulvestrant treatment. This could help them to predict the efficacy of endocrine therapy by monitoring the dynamic levels of ER in advance, and potentially help guide treatment of breast tumors in the future. 18F-FES was initially developed to image the primary breast tumor. In previous studies of 18F-FES conducted in humans, there were no adverse events (there have been no problems). While this is not the first time 18F-FES has been used in humans, it is the first study in which the investigators study its predictive value in the treatment efficacy in breast cancer.