A Phase III Clinical Study of HRS-6209 Plus Letrozole as First-line Therapy in Patients With Advanced or Metastatic Breast Cancer

The purpose of this study is to investigate the efficacy and safety of HRS-6209 in combination with letrozole compared with dalpciclib or palbociclib in combination with aromatase inhibitor in patients with advanced or metastatic breast cancer who have not received prior systemic treatment for advanced or metastatic disease. Approximately half of the participants will receive HRS-6209 plus letrozole while the other half of participants will receive dalpciclib or palbociclib in combination with aromatase inhibitor. The study team will monitor how each participant is doing with the study treatment during regular visits at the study clinic.