Impact of 18F-FES PET on the Therapeutic Treatment of Patients With Metastatic Breast Cancer

Inclusion Criteria:

1. Female aged at least 18 years old at the time of enrolment

2. Oestrogen-receptor positive primary breast cancer in IHC (ER ≥10%)

3. HER2-negative primary breast cancer (0, 1+, 2+ FISH negative)

4. Metastatic stage with at least one lesion identifiable on the conventional work-upother than a liver lesion

5. Patient relapsing under first-line treatment combining a CDK4/6inhibitor and hormonetherapy

6. Patient having undergone an FDG PET/CT during follow-up of first-line treatment formetastatic tumour revealing the relapse or undergoing a baseline FDG PET/CT seekingthe relapse during 2nd line staging (according to the recommendations of the Guideto Correct Use (GBU) for medical imaging tests). A period of 2 to 28 days will berespected between the 2 PET/CT scans (FDG/FES).

7. ECOG 0, 1 or 2

8. Life expectancy of at least 12 months

9. Patient registered with a Social Security scheme

10. Patient having signed an informed consent form

11. Patient able to follow the study procedures and fill in the quality of lifequestionnaires

Exclusion Criteria:

1. Isolated hepatic metastases (taking into account the high physiological hepaticuptake of FES)

2. Patients as first-line treatment for metastatic cancer or aftersecond-line treatmentfor metastatic cancer

3. Person presenting a known allergy to one of the components of EstroTep

4. Patients having been treated with a CDK4/6 inhibitor in combination with an SERM orSERD as first-line metastatic therapy

5. atients suffering from severe or known chronic liver or renal failure

6. Patient following a low-sodium diet or having alcohol consumption levelsincompatible with the administration of EstroTep, according to the investigator'sopinion

7. Woman of childbearing age with no effective means of contraception according to theinvestigator's opinion

8. Severe intercurrent disease or comorbidity assessed at risk

9. Persons referred to in articles L. 1121-5 to L. 1121-8 and L11222 of the FrenchPublic Health Code