The purpose of this study is to investigate the efficacy and safety of BGB-43395 in combination with letrozole compared with investigator's choice of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) in combination with letrozole in patients with advanced or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer (BC) who have not received prior systemic treatment for advanced or metastatic disease.
Participants must be at least 18 years of age or the legal age of consent in the jurisdiction in which the study is taking place at the time of signing the informed consent.
Participants with histologically confirmed locally advanced or metastatic HR+ HER2- breast cancer.
Participants must have a stable Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 1.
Adequate organ function.
Participants who have received prior systemic treatment in the advanced or metastatic setting.
Participants who have received prior treatment with any selective cyclin-dependent kinase 4 (CDK4) or cyclin-dependent kinase 2 (CDK2) targeting agent, or any other investigational anticancer drug in any disease setting, except for prior investigational or approved SERDs in the adjuvant setting, provided that disease recurrence occurred more than 12 months after the last dose of endocrine-based therapy.
Participants with active leptomeningeal disease or uncontrolled, untreated brain metastasis.
Parallel
BGB-43395
DrugAdministered orally.
Letrozole
DrugAdministered orally.
Abemaciclib
DrugAdministered orally.
Palbociclib
DrugAdministered orally.
Ribociclib
DrugAdministered orally.
Progression-Free Survival (PFS) Determined by Blinded Independent Central Review (BICR)
PFS is defined as the time from first dose until first documentation of progression or death, whichever comes first, as assessed by BICR per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
Overall Survival (OS)
OS is defined as the time from the date of randomization until the date of death due to any cause.
Overall Response Rate (ORR)
ORR is defined as the percentage of participants who had a complete response (CR) or partial response (PR), as assessed by BICR per RECIST v1.1.
Duration of Response (DOR)
DOR is defined as the time from the first occurrence of a documented objective response to the time of disease progression or death from any cause, whichever occurs first, as assessed by BICR per RECIST v1.1.
PFS Determined by Investigator
PFS is defined as the time from first dose until first documentation of progression or death, whichever comes first, as assessed by the investigator per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
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