This is a biomedical study of interventional type. The trial will include 270 patients (180 patients in the first cohort and 90 patients in a second cohort) over a period of 3 years + 2 years of follow up.

This prospective study will be conduct in patients who will receive a third line chemotherapy for metastatic breast cancer.

The main objective of the study (first cohort) is to identify patients who benefit from a third line treatment in terms of overall survival with a score established from clinical, histological, but also biological "classic" and "innovative" (account of circulating tumor cells) criteria, all of these criteria must be measurable before the introduction of the 3rd line.

This score will then be validated on the 2nd cohort.

There will be no interruption of inclusions between first and second cohort of patients

Inclusion Criteria:

1. Women of more than 18 years old
2. WHO 0-4
3. Metastatic breast cancer
4. Progression after two lines of chemotherapy with treatment decision by investigator to start a third-line chemotherapy
5. Evaluable disease
6. Histology: breast carcinoma whatever the histological type, grade, hormone receptor expression and HER-2
7. Patient able to complete the EORTC PAL 15 Questionnaire
8. Patient member in a national insurance scheme
9. Informed consent obtained and signed by the patient

Exclusion Criteria:

1. History of other (s) cancer (s) potentially metastatic (s)
2. Woman participating in a third line chemotherapy clinical trial
3. Pregnant women or nursing mothers can not participate in the study
4. Patient under legal guardianship
5. Patient unable to undergo medical test for various reasons including social or psychological reasons.