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.