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

• Taking blood samples before starting treatment (Other): For patient included in the metastatic breast cancer and prostate cancer, a blood sample will be taken (37 mL in total) for the CTCs detection using the 3 technologies (CellSearch®, Parsortix® and SmartCatch®). For 3 patients only, an additional blood volume (18 mL) will also be collected for tcDNA detection (exploratory analysis of 3 patients). For patient included in the metastatic breast cancer complementary cohort, a blood sample will be taken (56 mL in total) for the CTCs detection using Parsortix® and SmartCatch® technologies.

Primary outcomes

• The rate of patients with at least one additional CTC detected by the SmartCatch® method compared with the standard approach (CellSearch®). [15 months after the study start]: It is defined by the ratio of the number of patients with at least one additional CTC detected by the SmartCatch® method compared with the standard approach (CellSearch®) to the total number of patients.

Secondary outcomes

• The rate of patients with CTCs (CK+/CD45-) detected by each technique (CellSearch®, Parsortix® and SmartCatch®). [15 months after the study start]: This is defined as the ratio of the number of patients with CTCs detected by the technique to the total number of patients.
• The number of total CTCs (EpCAM+/CK+/CD45- and EpCAM-/CK+/CD45-) detected by the different techniques (CellSearch®, Parsortix® and SmartCatch®). [15 months after the study start]

Other outcomes

• The rate of patients with CTCs (CK+/CD45-) detected using different tubes by Parsortix® and SmartCatch® technologies. [15 months after the study start]

Sex: All, ages: 18 Years to any

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.