A Study Of Palbociclib (PD-0332991) + Letrozole VS. Placebo+ Letrozole For 1st Line Treatment Of Asian Postmenopausal Women With ER+/HER2- Advanced Breast Cancer [PALOMA-4]

Inclusion Criteria:

1. Adult Asian women with locoregionally recurrent or metastatic disease not amenable to curative therapy
2. Confirmed diagnosis of ER positive breast cancer
3. No prior systemic anti-cancer therapy for advanced ER+ disease
4. Postmenopausal women
5. Measurable disease as per Response Evaluation Criterion in Solid Tumors [RECIST] or bone-only disease
6. Eastern Cooperative Oncology Group [ECOG] 0-1
7. Adequate organ and marrow function
8. Patient must agree to provide tumor tissue

Exclusion Criteria:

1. Confirmed diagnosis of HER2 positive disease
2. Patients with advanced, symptomatic, visceral spread that are at risk of life threatening complication in the short term
3. Known uncontrolled or symptomatic CNS metastases
4. Prior neoadjuvant or adjuvant treatment with a non steroidal aromatase inhibitor (ie, anastrozole or letrozole) with disease recurrence while on or within 12 months of completing treatment
5. Prior treatment with any CDK 4/6 inhibitor