A Phase III Study of ESG401 for Locally Advanced or Metastatic HR+/HER2- Breast Cancer

Inclusion Criteria:

• Individuals able to understand and give written informed consent.

• Males or females aged ≥ 18 years ;

• Histologically and/or cytologically confirmed HR+/HER2- breast cancer who had failedat least one line of systemic chemotherapy in metastatic settings;

• Patients who are eligible for a chemotherapy regimen in the control group;

• Patients with at least one measurable lesion per RECIST 1.1 criteria;

• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 1;

• Expected survival ≥ 12 weeks;

• Patients with adequate organ and bone marrow function;

• Female patients of childbearing potential and male patients with partners ofchildbearing potential who use effective medical contraception from the time ofsigning the informed consent form until 180 days after the last dose.

Exclusion Criteria:

• Received chemotherapy, targeted therapy, immunotherapy, interventional therapy orother systemic anti-cancer therapie within 4 weeks before the first investigationalproduct administration;

• Toxicities from prior anti-tumor therapy not recovering to ≤ Grade 1;

• Received major surgeries 4 weeks prior to the first dose of study treatment orplanned to receive major surgeries during the study ;

• Prior topoisomerase I inhibitor therapy, including antibody-drugconjugate(ADC)therapy, or prior TROP2 targeted therapy, or use of any investigational anti-cancerdrug within 28 days or 5 half-lives before the first investigational productadministration;

• New thromboembolic events, intestinal obstruction, gastrointestinal bleeding orperforation within 6 months;

• Uncontrolled systemic bacterial, viral or fungal infections;

• Subjects with symptomatic or untreated CNS metastases, or those requiring ongoingtreatment for CNS metastases;

• Patients with Primary CNS malignancy；or patients with other malignancies within 3years prior to the first dose;

• Patients with uncontrollable systemic diseases;

• Patients with gastrointestinal diseases (such as chronic gastritis, chronicenteritis or gastric ulcers), or with a previous history of severe or chronicdiarrhea;

• Subjects with clinically significant cardiovascular disease;

• Human Immunodeficiency Virus (HIV) infection;

• Active hepatitis B or hepatitis C;

• Known immediate or delayed hypersensitivity reaction to irinotecan or othercamptocampin derivatives such as topotecan or to have had grade ≥3 gastrointestinalreactions associated with irinotecan, or allergies, or to any investigational drugor excipient ingredient;

• Pregnant or lactating women.