Main objective: Compare the response rate after 6 months of hormone treatment (or a major change in hormone treatment) in metastatic breast cancer, according to the uptake of FES in metastatic lesions taking-up FDG on PET/CT at baseline.~Secondary objectives:~evaluate diagnostic performance of FES PET/CT~determine whether FES PET/CT is able to detect metastases that are not visible on FDG PET/CT. This point may constitute a direct benefit for the patient~precise the nature of discordant FES/FDG foci~validate and improve the interpretation criteria for FES PET/CT~confirm the perfect tolerance
Compare the response rate after 6 months of hormone treatment (or a major change in hormone treatment) in metastatic breast cancer, according to the uptake of FES in metastatic lesions taking-up FDG on PET/CT at baseline. Hypothesis: best response rate will be observed in patients with all metastases taking up FES prior to treatment.