A Phase III Study of SKB264 for Locally Advanced, Recurrent or Metastatic HR+/HER2- Breast Cancer

Inclusion Criteria: Males or females aged ≥ 18 to ≤ 75 years at the time of signing the ICF; Histologically and/or cytologically confirmed HR+/HER2- breast cancer based on pathology reports on recent biopsy specimens or other pathological samples; Patients who had failed at least one line of systemic chemotherapy in unresectable locally advanced, recurrent, or metastatic stage; Patients with at least one measurable lesion per RECIST 1.1 criteria; those with only skin or bone lesions cannot be included; Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 1; Expected survival ≥ 12 weeks; Adequate organ and bone marrow function; Patients who are eligible for a chemotherapy regimen in the control group; Female patients of childbearing potential and male patients with partners of childbearing potential who use effective medical contraception from the time of signing the informed consent form until 6 months after the last dose; Patients who voluntarily participate in the study and sign the ICF, and able to comply with the visit and related procedures stipulated in the plan. Exclusion Criteria: Patients with a history of central nervous system (CNS) metastases or current CNS metastases； Patients with other malignancies (except cured basal or squamous cell skin cancer or carcinoma in situ of the cervix) within 3 years prior to the first dose; Patients with any cardio cerebral Vascular disease or cardio cerebral vascular risk factors may affect investigational treatment; Uncontrollable systemic diseases assessed by the investigator; History of (noninfectious) interstitial lung disease (ILD)/noninfectious neumonitis requiring steroid therapy and current ILD/noninfectious pneumonitis, or ILD/noninfectious pneumonitis at screening that cannot be excluded by imaging; Clinically serious lung injuries caused by lung diseases; Patients with active chronic Inflammatory bowel disease, gastrointestinal obstruction, severe ulcer, gastrointestinal perforation, abdominal abscess or acute gastrointestinal bleeding; Toxicities from prior anti-tumor therapy not recovering to ≤ Grade 1; Active hepatitis B or hepatitis C; Human immunodeficiency virus (HIV) antibody test positive or a history of acquired immunodeficiency syndrome (AIDS), known active syphilis infection; Known allergy or hypersensitivity to SKB264, or the excipients of SKB264; Prior TROP2 targeted therapy, prior topoisomerase I inhibitor therapy, including antibody-drugconjugate(ADC) therapy; Patients who received major surgeries 4 weeks prior to the first dose of study treatment or planned to receive major surgeries during the study ; Patients with concomitant infections requiring systemic antibiotic therapy within 2 week prior to the first dose of study treatment; Patients who have received live vaccines within 30 days prior to the first dose, or are scheduled to receive live vaccines during the study; Pregnant or lactating women.