A Randomized, Open Label, Phase III Trial to Evaluate the Efficacy and Safety of Palbociclib + Anti-HER2 Therapy + Endocrine Therapy vs. Anti-HER2 Therapy + Endocrine Therapy After Induction Treatment for Hormone Receptor Positive (HR+)/HER2-Positive Metastatic Breast Cancer


The primary objective of this study is to demonstrate that the combination of palbociclib with anti-HER2 therapy plus endocrine therapy is superior to anti-HER2-based therapy plus endocrine therapy alone in improving the outcomes of subjects with hormone receptor-positive, HER2+ metastatic breast cancer.

Study Arms

  • Experimental: Arm A - Palbociclib 125 mg daily + AntiHER2 Therapy (trastuzumab/pertuzumab) q3wks + Endocrine Therapy (letrozole, anastrozole, exemstane OR fulvestratnt) until confirmed disease
  • Active Comparator: Arm B - AntiHER2 Therapy (trastuzumab/pertuzumab) q3wks + Endocrine Therapy (letrozole, anastrozole, exemstane OR fulvestrant) until confirmed disease progression


  • Participants must have histologically confirmed invasive breast cancer that is metastatic or not amenable for resection or radiation therapy with curative intent. Histological documentation of metastatic/recurrent breast cancer is not required if there is unequivocal evidence for recurrence of the breast cancer.
  • Patients must have histologically confirmed HER2+ and hormone receptor positive (ER+ and/or PR+), metastatic breast cancer. ER, PR and HER2 measurements should be performed according to institutional guidelines, in a CLIA-approved setting in the US or certified laboratories for Non-US regions. Cut-off values for positive/negative staining should be in accordance with current ASCO/CAP (American Society of Clinical Oncology/College of American Pathologists) guidelines.
  • Patients must agree to provide a representative formalin-fixed paraffin-embedded (FFPE) tumor tissue block (preferred) from primary breast or metastatic site (archival) OR at least 15 freshly cut unstained slides from such a block, along with a pathology report documenting HER2 positivity and hormone receptor positivity.
  • Patients should be willing to provide a representative tumor specimen obtained from metastatic disease if clinically feasible. This is a recommended but optional research biopsy.