Breast cancer is a major public health issue despite therapeutic advances, it is the first cause of death cancer of women in Europe. Several treatments may be proposed depending on the general condition of the patient, the characteristics of the initial tumor and the stage of the disease. The different treatments in metastatic relapse of hormone receptor-positive breast cancer are systemic treatments, such as hormone therapy, chemotherapy, targeted therapies, and possible supportive care, but also in some cases local treatments such as surgery and radiotherapy. Comparative analysis of primary mammary tumors and their metastases has demonstrated the essential role of tumor heterogeneity, both in time and space, in the progression of the disease and the occurrence of resistance to treatments. Taking into account this intratumoral heterogeneity represents a major axis of improvement in the management of patients with breast cancer. The use of innovative radiotracers such as 16α- \[18F\] -fluoro-17β-estradiol (FES) may allow in the future to better evaluate this tumor heterogeneity in patients with metastatic breast cancer through non-metastatic characterization. invasive different lesions. It will be possible to propose to each patient a more personalized care with possibly the administration, in addition to the systemic treatment, of a local treatment adapted to the characteristics of some secondary lesions likely to respond less well to the systemic treatment. In this pilot study, the investigators would like to estimate the number of patients and the number of metastatic sites affected by tumor heterogeneity of estrogen receptor expression, which could benefit from specific management. This study will concern a population of patients with first metastatic recurrence of hormone receptor-positive breast cancer initially, with at least one metastasis, who are candidates for treatment with hormone therapy.