PATINAPalbociclib with Anti-HER2 Therapy and Endocrine Therapy for Hormone Receptor Positive (HR+)/HER2-Positive Metastatic Breast Cancer

This is a phase 3 treatment trial for individuals with a specific type of breast cancer known as Hormone Receptor Positive (HR+) and HER2-Positive Metastatic Breast Cancer. The study aims to evaluate the effectiveness and safety of adding an experimental drug, Palbociclib, to the current treatment regimen of anti-HER2 therapy and endocrine therapy. The goal is to understand if Palbociclib can delay the onset of therapeutic resistance and prolong the survival of patients. This study focuses on those with HER2+ disease who are also hormone receptor positive (HR+), as it's believed that Palbociclib may help overcome endocrine resistance in these patients and enhance the benefits of anti-HER2 therapy. Participants in this trial will be randomly assigned to one of two groups. One group will receive Palbociclib along with their current anti-HER2 therapy and endocrine therapy, while the other group will continue with only the anti-HER2 therapy. The primary outcome measured in this study is Progression-free Survival (PFS), which is the time from the start of the study until the disease worsens or the participant passes away. The study also includes a detailed molecular examination of the disease at the start, allowing researchers to explore the benefits of Palbociclib in specific subsets of HER2+/HR+ disease, such as those with PIK3CA mutant.