This is a Phase III, randomized, open-label, 2-arm, multicentre, international study assessing the efficacy and safety of FDA018-ADC compared with Investigator's Choice Chemotherapy(ICC) in participants with locally recurrent inoperable or metastatic Triple-negative Breast Cancer(TNBC) who are resistant to, or recurring during or after taxane therapy.

The primary objectives of the study are to demonstrate the superiority of FDA018-ADC relative to ICC by assessment of PFS per Blinded Independent Central Review(BICR) and OS in participants with locally recurrent inoperable or metastatic TNBC who are resistant to, or recurring during or after taxane therapy.

Inclusion Criteria:

1. Patients capable to give written informed consent;
2. Histologically or cytologically confirmed TNBC based on the most recent analyzed biopsy or other pathology specimen. Triple negative is defined as <1% expression for estrogen receptor (ER) and progesterone receptor (PR) and negative for human epidermal growth factor receptor 2 (HER2) by in-situ hybridization;
3. Prior exposure to a taxane in localized or advanced/metastatic setting, and recurred during or after treatment;
4. Eligible for one of the chemotherapy options listed as ICC (eribulin, capecitabine, gemcitabine, or vinorelbine) as per investigator assessment;
5. Have measurable lesions defined in RECIST v.1.1, those with only skin or bone lesions cannot be included;
6. Expected survival≥3 months;
7. Eastern Cancer Cooperative Group (ECOG) performance status 0-1;
8. Adequate bone marrow, hepatic, and renal function;
9. All acute toxicity of previous anti-tumor treatment or surgery is relieved to baseline severity or NCI CTCAE version 5.0≤1;
10. Subjects could provide tumor tissues or tissue specimens;
11. Patients of child bearing potential must agree to take contraception during the study and for 6 months after the last day of treatment.

Exclusion Criteria:

1. Patients with other malignancies, except cured basal or squamous cell skin cancer or in situ cancer of cervix; and patients with other malignancies must have a tumor-free period of at least 5 years;
2. Have central nervous system metastasis with clinical symptoms;
3. Have history of clinical significant active chronic obstructive pulmonary disease, or other moderate-to-severe chronic respiratory illness present within 6 months prior to the first dose;
4. Suffering from active chronic inflammatory bowel disease (ulcerative colitis, Crohn disease), and history of intestinal obstruction, or Gl perforation;
5. Patients with Gilbert's disease or heterozygous for the UGT1A1*28 allele;
6. Participants known to be human immunodeficiency (HIV) positive, hepatitis B positive, or hepatitis C positive;
7. Patients who have received prior TROP-2-targeted therapy;
8. Patients who have received prior topoisomerase I inhibitor contained therapy;
9. Received other anti-tumor treatments (including chemotherapy, radiotherapy, targeted therapy, immunotherapy, experimental treatment and so on) within 4 weeks prior to the first dose;
10. Patients who have received live vaccines within 4 weeks prior to the first dose;
11. Patients who had undergone major surgery or severe trauma within 4 weeks prior to the first dose;
12. Patients who had undergone systemic high-dose steroids within 2 weeks prior to the first dose;
13. Patients have history of psychotropic drug abuse, alcohol or drug abuse;
14. Women who are pregnant or lactating;
15. Other circumstances that is deemed not appropriate for the study by investigator.