Omic Technologies to Track Resistance to Palbociclib in Metastatic Breast Cancer

Patients enrolled in the study will receive the following interventions: * Biospecimen sample collection: before and during treatment, and at progression * Tumor biopsy before treatment and at progression The aim of this study is to describe molecular changes associated with resistance to Palbociclib at the individual level and describe longitudinal changes in the profile of tumor, VOCs and exosomes according to treatment response. Other objectives of the study include: * Proportion of single or shared molecular alterations / signatures between patients at progression time * Associations between tumor signatures, VOCs and exosomes * Compare molecular changes identified by proteomics with those observed by genomics / transcriptomics * Compare the evolution of VOCs and exosomes over time with evolution of liquid biopsy markers.