The goal of this clinical trial is to compare the objective response rates (ORR) of different doses of BL0175 in patients with postmenopausal hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer. The main questions it aims to answer are:
1. Which dose level of BL0175 demonstrates the optimal ORR? 2. What is the recommended phase 3 dose (RP3D) based on efficacy and safety data across the tested dose levels?
Voluntary participation in the trial, understanding the specific procedures of the trial, and willing to sign a written informed consent form.
Age ≥ 18 years.
HR positive, HER2 negative, with locally advanced or metastatic breast cancer in postmenopausal patients during or after endocrine therapy.
The blood pregnancy test result during the screening period must be negative (if the postmenopausal state is caused by GnRH agonists).
Participants with symptomatic central nervous system (CNS) metastases or cancerous meningitis;
Have a history of other primary malignant tumors (except for participants who have been cured of skin basal cell carcinoma, skin squamous cell carcinoma, or cervical carcinoma in situ, and participants with other primary tumors that have no evidence of disease for 2 years or more and do not require treatment).
Patients whose pericardial effusion, pleural effusion or ascites remain uncontrollable after intervention.
Participants who have a history of allogeneic transplantation (including but not limited to allogeneic organ, bone marrow, or stem cell transplantation).