A Phase II Randomized Study Evaluating the Biological and Clinical Effects of the Combination of Palbociclib With Letrozole as Neoadjuvant Therapy in Post-Menopausal Women With Estrogen-Receptor Positive Primary Breast Cancer

Inclusion Criteria

• Patients must be postmenopausal women defined as: Age 56 or older with no spontaneous menses for at least 12 months prior to study entry; or Age 55 or younger with no menses for at least 12 months prior to study entry (e.g., spontaneous or secondary to hysterectomy) and with a documented estradiol level in the postmenopausal range according to local institutional/laboratory standard; or Age greater than or equal to 18 with documented bilateral oophorectomy.
• Operable ER-positive/HER2- negative, invasive early breast cancer, suitable for neoadjuvant AI treatment. HER2-negative as determined by American Society of Clinical Oncology - College of American Pathologists (ASCO-CAP) guidelines.
• No known severe hypersensitivity reactions to compounds similar to palbociclib or palbociclib excipients or to endocrine treatments.
• A breast tumor with an ultrasound size of at least 2.0 cm.
• Patients must have the ability to swallow oral medication.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• At the time of randomization, blood counts performed within 4 weeks prior to randomization must meet the following criteria: absolute neutrophil count (ANC) must be greater than or equal to 1500/mm3; Platelet count must be greater than or equal to 100,000/mm3; Hemoglobin must be greater than or equal to 10 g/dL.
• international normalized ratio (INR) must be within normal limits of the local laboratory ranges.
• The following criteria for evidence of adequate hepatic function performed within 4 weeks prior to study entry must be met: total bilirubin must be less than or equal to upper limit of normal (ULN) for the lab unless the patient has a bilirubin elevation greater than ULN to 1.5 x ULN due to Gilbert's disease or similar syndrome involving slow conjugation of bilirubin; and alkaline phosphatase must be must be less than or equal to 1.5 x ULN for the lab; and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) must be less than or equal to 1.5 x ULN for the lab.
• Serum creatinine performed within 4 weeks prior to study entry must be less than or equal to 1.25 x ULN or estimated creatinine clearance less than 60 mL/min (as calculated using the method standard for the institutions).

Exclusion Criteria

• Active hepatitis B or hepatitis C with abnormal liver function tests.
• HIV positive patients receiving antivirals.
• Premenopausal or peri-menopausal women.
• Inflammatory/inoperable breast cancer.
• HER2-positive as determined using ASCO-CAP Guidelines.
• Concurrent use (defined as use within 4 weeks prior to baseline tissue sample being taken) of hormone replacement therapy (HRT) or any other estrogen-containing medication (including vaginal estrogens)
• Prior endocrine therapy for breast cancer.
• Any invasive malignancy within previous 5 years (other than basal cell carcinoma or cervical carcinoma in situ).
• Other nonmalignant systemic disease that would preclude the patient from receiving study treatment or would prevent required follow up such as: Active infection or chronic infection requiring chronic suppressive antibiotics; Malabsorption syndrome, ulcerative colitis, inflammatory bowel disease, resection of the stomach or small bowel, or other disease or condition significantly affecting gastrointestinal function; Chronic daily treatment with corticosteroids with a dose of greater than or equal to 10 mg/day methylprednisolone equivalent (excluding inhaled steroids); Seizure disorders requiring medication.
• Diagnosis by fine needle aspiration (FNA) alone or excisional biopsy or lumpectomy performed prior to study entry.
• Surgical axillary staging procedure prior to study procedure (with exception of FNA or core biopsy).
• Definitive clinical or radiologic evidence of metastatic disease.
• History of ipsilateral invasive breast cancer regardless of treatment or ipsilateral ductal carcinoma in situ (DCIS) treated with radiotherapy or contralateral invasive breast