A Phase II Study to Evaluate the Efficacy and Safety of HLX43 in Patients With Hormone Receptor Positive, HER2 Negative Locally Advanced or Metastatic Breast Cancer

Inclusion Criteria: 1. Male/female who are at least 18 years of age and and no more than 75 years old on the day of signing the informed consent. 2. With histologically confirmed diagnosis of HER2-negative, Hormone Receptor Positive Locally Advanced or Metastatic Breast Cancer. 3. Must have experienced disease progression after receiving at least one line of endocrine therapy for advanced or metastatic disease. 4. Had measurable disease according to the RECIST v1.1, the target lesion must not be a bone metastatic lesion only. 5. ECOG PS: 0-1. 6. Expected survival ≥ 6 months. 7. Had adequate organ function Exclusion Criteria: 1. Patients with other malignant tumors within 3 years before the randomization 2. Prior documented interstitial lung disease (ILD)/ pneumonitis that required steroids, current ILD/ pneumonitis, or suspected ILD/pneumonitis 3. Lung-specific intercurrent clinically significant illnesses 4. Uncontrolled or significant cardiovascular disease or infection 5. Prior adverse events leading to permanent discontinuation of immunotherapy; or prior immune-related pneumonia or immune-related myocarditis of grade ≥2.