Breast cancer is the most common cancer in woman. Aromatase inhibitors have demonstrated a real efficacy however a resistance to treatment exists.~ESR1 mutations appear like involved in the mechanism of resistance to aromatase inhibitors treatment.~The purpose of the study is to determine the frequency ESR1 mutations by Digital PCR in patient with metastatic breast cancer.~The significance of the Digital PCR technique will be determined first in plasma issued from healthy volunteers.~At the initiation of aromatase inhibitors treatment patient with metastatic breast cancer will be included in the study. During their follow-up visit every 3 months), their status towards their disease will be collected and a plasma will be collected too.~When the patient progress clinically or radiologically the plasma concomitant to this progression will be analysed by Digital PCR to detect ESR1 mutations.~The patient will be followed during 2 years.
The purpose of the study is to determine the frequency ESR1 mutations by Digital PCR in patient with metastatic breast cancer.