Combination of Palbociclib and aromatase inhibitor (Letrozole or Anastrozole)

This study is a multicenter, international, open-label phase II study. Based on inclusion/exclusion criteria, eligible pre and postmenopausal patients with newly diagnosed metastatic luminal hormone receptor-positive and HER2 negative breast cancer, will be prospectively treated with a standard combination of hormone therapy (Letrozole or Anastrozole) and Palbociclib. This combination will continue until progression. Treatment response will be evaluated every three months using clinical and radiological assessments (Revised RECIST guidelines). Patients will undergo serial liquid biopsies (blood tests) for plasma molecular fingerprinting by the Quantum Optics technology. This study will be the first program exploring the adjunction of the Quantum Optics technology on liquid biopsies to define individual 'molecular fingerprinting profiles' to predict the individual therapeutic effects of Palbociclib combined with Aromatase Inhibitors (AI) (plus ovarian function suppression (OFS) for pre/peri-menopausal patients) in luminal hormone receptor-positive and HER2 negative advanced breast cancer. Batteries of algorithmic tests will integrate the variables obtained by Quantum Optics (to evaluate the efficacy or not of the combination of Palbociclib + Aromatase Inhibitors (AI) ). This approach introduces the concept of singularity to break from the classic idea of "one size fits all".