This is a prospective, monocentric, proof of concept study aims to identify in prostate cancer patients, a potential relationship between CTC-PSMA positivity and 18F-PET-PSMA results as well as patient outcome. Patients with 18F-PET-PSMA indication will perform imaging extension work-up as part of current practice. If they agree to participate in the study, a blood sample will be performed prior to the 18F-PET-PSMA standard imaging (T1). In order to evaluate the potential relationship between CTC-PSMA and 18F-PET-PSMA imaging, the study will be presented to all patients seen in consultation for an extension workup for prostate cancer. This will allow to analyze the results in patients with different level of tumor burden afterward to define the following three groups based on imaging results: Group 1 : no tumor volume Negative 18F-PET-PSMA (patients without uptake lesion) Group 2 : low or medium tumor volume Positive 18F-PET-PSMA (patients with an uptake in prostate bed or with an oligo-metastatic extension (number of lesions \< 6)) Group 3 : high tumor volume Positive 18F-PET-PSMA (patients with a polymetastastatic extension (number of lesions ≥ 6)). In each of these groups, the rate of patients with positive PSMA CTC will be analyzed (i.e. patient having at least one CTC-PSMA positive). For patients with an indication of treatment by 177LuPSMA-617 (PLUVICTO®) according to standard practices, additional blood samples will also be collected at the following time points: 2nd cycle (T2) and 4th cycle of treatment (T3), just before injection. For these patients, data will be collected up to 6 months after the last treatment injection (clinical and biological data; results of tumor assessments based on 18F-PET-PSMA imaging).