Comparison of Different Methods of CAPTure of Circulating Tumour Cells (CTC) in Patients With Metastatic Breast or Prostate Cancer

Inclusion Criteria: 1. Patient with breast cancer (whatever the immunohistochemical subtype: triple-negative, RH+/HER2-negative or HER2-positive) or prostate cancer, multi-metastatic, eligible for a new line of treatment. 2. Patient not yet initiated on a new specific treatment for breast or prostate cancer at inclusion. 3. Age ≥ 18 years and WHO ≤ 2 4. Patient affiliated to Social Security scheme in France. 5. Patient having signed informed consent prior to inclusion in the study and prior to any study-specific procedures. Exclusion Criteria: 1. Associated pathology(ies) likely to prevent the study procedure from running smoothly 2. Any psychological, family, geographical or sociological condition that prevents compliance with the medical follow-up and/or procedures stipulated in the study protocol. 3. Patient deprived of liberty or under legal protection (guardianship, legal protection) 4. Patient who has had another solid tumor (excluding carcinoma in situ of the breast or cervix) within 5 years.