The Use of FES-PET Imaging as a Tool to Detect a Possible Reversion of Estrogen Receptor (ER)-α Status in Patients With Metastatic Breast Cancer HER2 + and ERα Neg Treated With Trastuzumab + Pertuzumab + Taxane.

This is an exploratory, prospective and multicentric study aiming to highlight by FES-PET imaging that an anti-HER2 treatment by trastuzumab + pertuzumab can reverse the ERα status in patients with metastatic breast cancer HER2 + and ERα neg. For each included patient, 2 FES-PET Imaging will be performed for the study (before cancer treatment initiation and before the cycle 3 of treatment) at the IUCT-O center (Institut Universitaire du Cancer de Toulouse). Treatment (trastuzumab + pertuzumab + taxane) will be administered according to the current recommendations in each participant center. Patients will be followed during the 3 cycles of treatment.