Almost 70% of breast tumors are endocrine responsive, as defined by estrogen receptor (ER) expression by immunohistochemistry on the primary tumor, with a demonstrated predictive value on response to endocrine therapy. However it can be estimated that roughly 30% of ER positive breast cancer patients will re lapse despite adjuvant endocrine therapy. Moreover, it has also been shown that 10 to 20% of metastatic breast cancer lesions lose completely or partially the expression of hormone receptors. The early identification of those patients with ER positive breast cancer, not sensitive to endocrine therapy might help to improve systemic treatment options, sparing patients from unnecessary toxicities and inactive drugs. The availability [18F]fluoro-oestradiol-17β (18F-FES), an oestradiol analogue labeled with F18, may allow to test in vivo the performance of oestrogen receptors, by testing their linkage ability. In metastatic breast cancer,18F-FES uptake by metastatic lesions has been proposed to be a better predictor of response to endocrine therapy than ER expression itself. The aim of this proposal is to validate thepredictive value of18F-FES uptake at PET/CT scan in metastatic ER positive patients. The study will be developed as follows:
1. Clinical validation trial: this is a phase II randomized comparative clinical trial with a diagnostic agent (18F -FES), whose primary aim is to identify endocrine resistant patients.
2. Translational study: this will include the evaluation of estrogen-related genes on primary tumor and biopsies of metastatic sites. Expression data will then be correlated with 18F-FES uptake results.