Study of the Impact of Everolimus Treatment on Lymphocytes NK (Natural Killer) Development and Functions for Patients With a Metastatic Breast Cancer (HR+ / HER2/Neu Negative)

Inclusion Criteria: * Women \> 18 years old * Metastatic breast cancer HR+ (Hormone Receptor positive), HER2/neu negative (Human Epidermal Growth Factor Receptor-2) * ECOG PS (Eastern Cooperative Oncology Group Performance Status) ≤2 * Eligible to an hormonotherapy treatment combined to an mTOR (mammalian Target Of Rapamycin) inhibitor (i.e. SPC (Summary of Product Characteristics) modalities) * Measurable disease according to RECIST 1.1 (Response Evaluation Criteria In Solid Tumors) * Not receiving the non-authorized concomitant treatments * Patient should understand, sign, and date the written voluntary informed consent form at the screening visit prior to any protocol-specific procedures performed. * Patients must be covered by a medical insurance Exclusion Criteria: * BMI\>30 * All dysimmune disease, history of transplantation or immunosuppressive therapy or corticotherapy * All chronic inflammatory diseases * Last chemotherapy \< 6 months * Corticotherapy \<1 year and more than 1 month * Restrictive diet ≤3 months before inclusion