Predicting Breast Cancer Endocrine Responsiveness Using Molecular Imaging.

The estrogen receptor (ER) is expressed on the vast majority of newly diagnosed breast cancers, yet not all ER-positive tumors will respond to endocrine therapy. Selecting patients for endocrine therapy can be considered as a series of predictive tests: does the tumor express the ER and if so, will the endocrine therapy interact with the target to produce a response? These are both challenges to which molecular imaging is functionally suited. Imaging of the ER has been most successful using 16-α[18F]-flouro-17β-estradiol (FES) positron emission tomography (PET). Functional imaging of the ER using FES-PET has been shown to be a predictive tool in determining response to endocrine therapy, and PET imaging of the ER can be used to measure the pharmacodynamic effect of ER-directed endocrine therapy. This article reviews the literature on FES-PET as a functional tool in predicting response to endocrine therapy in breast cancer and discusses future directions.