The purpose of this study is to compare any good and bad effects of using 2 years of Palbociclib in combination with standard anti-hormone therapy to using standard anti-hormone therapy alone and to evaluate the likelihood that invasive breast cancer returns.
- Pre- and postmenopausal women or men with Stage II or Stage III early invasive breast cancer
- Patients must have undergone breast surgery for the current malignancy. FFPE tumor tissue block must be confirmed to be received at the central sample repository prior to randomization
- Patients with Stage I or IV breast cancer are not eligible
- Prior therapy with any CDK inhibitor.
Participants will either be in Arm A or Arm B. Arm A is the experimental arm with Palbociclib given at a dose of 125 mg orally once daily, Day 1 to Day 21 followed by 7 days off treatment in a 28-day cycle for a total duration of 2 years, in addition to standard adjuvant endocrine therapy for a duration of at least 5 years. Arm B participants will receive standard adjuvant endocrine therapy for a duration of at least 5 years. Participants will also have bloods draws and take part in questionnaires for this study.