Molecular Alterations Associated With Resistance to Endocrine Therapy and Impacting Treatment With mTOR Inhibitor

Inclusion Criteria: \- Eligible for everolimus+exemestane treatment as required by the marketing authorisation conditions 1. Women (or men) with histologically-proven Estrogen Receptor-positive (ER+) and/or Progesterone Receptor-positive (PR+) / Human Epidermal growth factor Receptor 2-negative (HER2-) metastatic breast adenocarcinoma or locally advanced disease who cannot be treated with surgery and/or radiation therapy 2. Postmenopausal women 3. Asymptomatic if visceral disease 4. Second line hormonotherapy or more for metastatic or locally advanced disease after recurrence or progression following a non-steroidal aromatase inhibitor (in adjuvant or metastatic setting) \- Eligible for the biopsy 5. Progressive disease under endocrine therapy at the time of inclusion 6. Treatment with everolimus and exemestane not yet started 7. Patients with metastases that can be biopsied, except bone metastases 8. Measurable or evaluable disease 9. Age ≥18 years 10. WHO Performance Status 0/1 11. Provision of signed and dated, written informed consent prior to any protocol specific procedure, including biopsy 12. Patient with social insurance coverage Exclusion Criteria: 1. Contraindications for everolimus+exemestane treatment 2. Previous treatment with an anti-mTOR therapy 3. More than 1 previous line of chemotherapy in metastatic setting 4. Life expectancy \<3 months 5. Spinal cord compression and/or symptomatic or progressive brain metastases (unless asymptomatic or treated and stable off steroids for at least 30 days prior to start of study drug) 6. Haematopoietic function or organ impairment as shown by the following criteria: * Polynuclear neutrophils \<1.5 x 10⁹/L * Platelets \<100 x 10⁹/L * Haemoglobin \<90 g/L * Alanine aminotransferase (ALAT) / aspartate aminotransferase (ASAT) \>2.5 x ULN in the absence of or \>5 x upper limit of normal (ULN) in the presence of liver metastases * Bilirubin \>1.5 x ULN * Creatinine clearance ≤50 mL/min (measured or calculated by Cockcroft and Gault formula) * Calcium and phosphate \>ULN 7. Abnormal coagulation or any other medical situation contraindicating biopsy 8. Bone metastases when this is the only site of biopsiable disease 9. Any condition which in the Investigator's opinion makes it undesirable for the subject to participate in the trial or which would jeopardize compliance with the protocol 10. Individuals deprived of liberty or placed under the authority of a tutor