Study to Determine the Utility of FES-PET in the Prediction of Response to Fulvestrant in Women With Estrogen Positive Metastatic Breast Cancer

More than 70% of patients with metastatic breast cancer present with hormone receptor positive disease and for whom hormonal therapy is the preferred treatment approach. First-line treatment recommendations for women with hormone receptor positive locally advanced or metastatic disease includes a generation aromatase inhibitors or tamoxifen. Fulvestrant, a 17β-estradiol analog, is an antiestrogen that suppresses estrogen signaling by binding to ER and inducing oestrogen receptor degradation and has estrogen antagonistic activity but no estrogen agonistic effect. Fulvestrant has been shown to have superiority over other endocrine therapy in a series of randomized controlled trials. The whole-body imaging of the availability of ER using FES-PET may prove valuable to evaluate the effects of fulvestrant on the ER non-invasively in individual patients. This potentially allows early prediction of therapy efficacy to fulvestrant in women with estrogen positive metastatic breast cancer. In this pilot-study we will evaluate 35 patients who received fulvestrant as treatment for metastatic breast cancer. All patients will undergo FES-PET/CT at baseline and FES-PET after 28 days. Whenever possible, tumor biopsies will be performed to correlate to FES-PET results.