PAlbociclib Plus Tamoxifen for the Treatment of Hormone Receptor-positive, HER2-negative Advanced Breast Cancer Women - Asian studY

Inclusion Criteria:

1. Women 18 years of age or older with histologically or cytologically proven locally advanced or metastatic breast cancer, not amenable to resection or radiation therapy with curative intent
2. Documented diagnosis of HR+/HER2- breast cancer
3. Any menopausal status
4. Previously untreated with any endocrine therapy for their HR+/HER2- advanced breast cancer; or progressed while on or within 3 month from prior endocrine therapy other than tamoxifen for advanced breast cancer. If patients have adjuvant endocrine therapy, they must satisfy as follows: progressed 12 months or more since prior adjuvant endocrine therapy with tamoxifen; or progressed during or after adjuvant endocrine therapy with an aromatase inhibitor.
5. Measurable disease or non-measurable disease as defined by RECIST ver.1.1
6. Eastern Cooperative Oncology Group (ECOG) PS 0-1
7. Adequate organ and marrow function, resolution of all toxic effects of prior therapy or surgical procedures

Exclusion Criteria:

1. Prior treatment with any CDK inhibitor, tamoxifen, everolimus, or agent that inhibits the PI3K-mTOR pathway
2. Patients with extensive advanced/metastatic, symptomatic visceral disease, or known uncontrolled or symptomatic CNS metastases
3. Use of strong or moderate CYP3A4 and/or CYP2D6 inhibitors or inducers
4. Major surgery or any anti-cancer therapy within 2 weeks of randomization
5. Prior stem cell or bone marrow transplantation