The aim of this study is to evaluate the efficacy and safety of ESG401 as first-line treatment in patients with unresectable recurrent or metastatic triple-negative breast cancer.

This is a randomized, open-label, multicenter Phase 3 study to evaluate ESG401 versus Investigator's Choice Chemotherapy (ICC) as first-line treatment in subjects with unresectable recurrent or metastatic triple-negative breast cancer.

Key Inclusion Criteria:

1. Males or females aged ≥ 18 years ;
2. Histologically and/or cytologically confirmed TNBC;
3. De novo metastatic or relapsed ≥ 6 months post completion of treatment with curative intent;
4. No prior systemic anti-cancer therapy for unresectable recurrent or metastatic disease;
5. Participants whose tumours are PD-L1-negative, or Participants whose tumours are PD-L1-positive and have relapsed after prior PD-1/PD-L1 inhibitor therapy for early-stage breast cancer, or comorbidities precluding PD-1/PD-L1 inhibitor therapy;
6. Eligible for the chemotherapy options listed as investigator's choice chemotherapy (paclitaxel, nab-paclitaxel, capecitabine, eribulin, or carboplatin) as assessed by the investigator;
7. At least one measurable lesion per RECIST v1.1;
8. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 with no worsening within 2 weeks prior to randomization;
9. A life expectancy of at least 12 weeks;
10. Adequate organ and bone marrow function.

Key Exclusion Criteria:

1. Use of any investigational anti-cancer drug within 28 days or 5 half-lives before the first investigational product administration.
2. Toxicities from prior anti-tumor therapy not recovering to ≤ Grade 1.
3. Prior topoisomerase I inhibitor therapy, including antibody-drug conjugate(ADC) therapy, or prior TROP2 targeted therapy.
4. New thromboembolic events, intestinal obstruction, gastrointestinal bleeding or perforation within 6 months.
5. Subjects with symptomatic or untreated CNS metastases, or those requiring ongoing treatment for CNS metastases.
6. Patients with Primary CNS malignancy, or patients with other malignancies within 3 years prior to the first dose.
7. Patients with uncontrollable systemic diseases.
8. Patients with gastrointestinal diseases (such as chronic gastritis, chronic enteritis or gastric ulcers), or with a previous history of severe or chronic diarrhea.
9. Subjects with clinically significant cardiovascular disease.
10. Human Immunodeficiency Virus (HIV) infection.
11. Active hepatitis B or hepatitis C.
12. Known immediate or delayed hypersensitivity reaction to irinotecan or other camptocampin derivatives such as topotecan or to have had grade≥3 gastrointestinal reactions associated with irinotecan, or allergies, or to any investigational drug or excipient ingredient.
13. Pregnant or lactating women.