PALbociclib CoLlaborative Adjuvant Study: A Randomized Phase III Trial of Palbociclib With Standard Adjuvant Endocrine Therapy Versus Standard Adjuvant Endocrine Therapy Alone for Hormone Receptor Positive (HR+) / Human Epidermal Growth Factor Receptor 2 (HER2)-Negative Early Breast Cancer

Open to people ages 18 years and up

• Signed informed consent prior to study specific procedures.
• Age ≥18 years (or per national guidelines).
• Pre- and postmenopausal women or men with Stage II (Stage IIA limited to max. 1000 patients) or Stage III early invasive breast cancer
• Patients with multicentric and/or multifocal and/or bilateral early invasive breast cancer are eligible if all histopathologically examined tumors meet pathologic criteria for ER+ and/or PR+ and HER2-.
• Patients must have histologically confirmed ER+ and/or PR+, HER2-, early invasive breast cancer.
• Patients must have undergone adequate (definitive) breast surgery for the current malignancy.

FFPE tumor tissue block must be confirmed to be received at the central sample repository prior to randomization.

• ECOG performance status 0-1.
• Patients must be able and willing to swallow and retain oral medication.
• Serum or urine pregnancy test must be negative in premenopausal women within 14 days of randomization, or in women with amenorrhea of less than 12 months at time of randomization.
• Patients who received neo/adjuvant therapy must be after last dose of chemotherapy and/or biologic therapy and must have sufficient resolution of side effects.
• Patients who received breast/axilla/post-mastectomy chest wall radiotherapy must be after last dose of radiotherapy and must have sufficient resolution of side effects.
• Patients must have sufficient resolution of any surgical side effects (no active wound healing complications).

-Patients must either be initiating or have already started adjuvant hormonal treatment. -

• Patients who already received neo/adjuvant endocrine therapy are eligible as long as they are enrolled within 12 months of initial histological diagnosis and after completing no more than 6 months of adjuvant endocrine therapy.
• Absolute neutrophil count ≥ 1,500/µL
• Platelets ≥ 100,000/ mm3
• Hemoglobin ≥ 10g/dL
• Total serum bilirubin ≤ ULN; or total bilirubin ≤ 3.0 × ULN with direct bilirubin within normal range in patients with documented Gilbert's Syndrome.
• Aspartate amino transferase (AST or SGOT) and alanine amino transferase (ALT or SGPT)≤ 1.5 × institutional ULN.
• Serum creatinine below the upper limit of the institutional normal range (ULN) or creatinine clearance ≥ 60 mL/min/1.73 m2 for patients with serum creatinine levels above institutional ULN.