Purpose: 18F-Fluoroestradiol [18F]FES has emerged as a valuable PET tracer to predict the response to hormone therapy in recurrent or metastatic breast cancer patients. A clinically acceptable product requires a rapid reliable synthesis and must be demonstrated to maintain chemical stability and receptor specific uptake during patient studies. [18F]FES then becomes a dependable tracer for the evaluation and management of breast cancer patients.
Methods: An improved automated radiosynthesis of [18F]FES was developed. Stability studies of the injectible form of [18F]FES were performed up to 24 h after dose formulation under normal storage conditions. A comparative FES/FDG PET imaging in ER+ breast cancer patients is reported.
Results: The improved synthesis procedure utilizes fewer hydrolysis steps and a single high performance liquid column chromatography (HPLC) purification of the labeled mixture affording [18F]FES in good yield with high radiochemical purity (>99%). Stability studies with purified [18F]FES in saline/ethanol (85:15 v/v) indicated no radiolytic or chemical degradation of this radiopharmaceutical when stored for 24 h at 20-24 degrees C. Positron Emission Tomography (PET) studies with [18F]FES and [18F]FDG in estrogen receptor positive (ER+) breast cancer patients indicated that while FDG accumulation was seen in all metabolically hyperactive sites, the uptake of FES clearly delineated the ER+ tissues regions.
Conclusions: An improved automated synthesis of [18F]FES has been developed and the integrity of this product has been validated by long term stability studies and clinical PET imaging studies in ER+ breast cancer patients. A lack of concordance between FES and FDG uptake in a patient with metastatic breast cancer suggests specificity of the FES for tumors expressing estrogen receptors.