Study of Palbociclib and Trastuzumab With Endocrine Therapy in HER2-positive Metastatic Breast Cancer

After the amendment of PATRICIA study, two additional cohorts will be included: * Cohort C1: will include patients with OR+, HER2 positive, Luminal intrinsic subtype determined by PAM50 who will receive trastuzumab + palbociclib + endocrine therapy (ET) * Cohort C2: will include patients with OR+, HER2 positive, Luminal intrinsic subtype determined by PAM50 who will receive treatment of physician's choice. When the recruitment of those cohorts C begins, the recruitment in cohorts A and B will be closed. For cohorts C, an adaptive design will be applied to compare arms of treatment in patients with Luminal subtype locally advanced or metastatic breast cancer (MBC). All patients in those cohorts will have histologically- confirmed HR+/HER2-positive and PAM50-confirmed Luminal intrinsic subtype breast adenocarcinoma, and must have received at least 1 previous line of sistemic treatment for locally advanced disease or MBC which must have included trastuzumab and/or anti-HER2 Antibody-Drug conjugate. Stratification factors will include number of previous regimens for advanced breast cancer (one and two vs three or more) and presence of visceral disease (yes vs no). Treatment in all cohorts will be administered until progression, unacceptable toxicity, patient consent withdrawal, or death A total of 102 patients will be included. The inclusion period will be divided in two phases. During phase I it is planned to include 45 patients in 24 months; considering early stopping rule according to SF rate. During phase II, the trial will continue until the final evaluable number of 102 randomizations are included.