Phase III clinical trial - Sein métastatique HER2+

Subjects will be randomized into one of two treatment arms following minimum of 4 and maximum of 8 cycles of induction treatment with anti-HER2 therapy. Arm A subjects will receive the experimental therapy, palbociclib, in addition to their current anti-HER2 therapy and endocrine therapy. Arm B subjects will continue to receive the anti-HER2 therapy. It is expected that the addition of palbociclib to the first-line treatment of HER2 disease will delay the onset of therapeutic resistance and ultimately prolong the survival of patients with metastatic breast cancer. The study is designed to treat the subset of patients with HER2+ disease who are also hormone receptor positive (HR+). It is also expected that palbociclib will modulate the endocrine resistance in HER2+/HR+ disease and potentiate the benefits of anti-HER2 therapy. Lastly, the current study includes a comprehensive molecular characterization of the disease at study entrance which will allow us to investigate the benefits of palbociclib in subsets of HER2+/HR+ disease such as PIK3CA mutant.