A Study of 9MW2821 Versus Chemotherapy in Participants With Previously Treated Locally Advanced or Metastatic Triple-Negative Breast Cancer

Inclusion Criteria: * Competent to comprehend, sign, and date an independent ethics committee/institutional review board/research ethics board (IEC/IRB/REB) approved informed consent form. * Male or female subjects aged 18 to 75 years (including 18 and 75 years). * ECOG 0-1. * Histopathological diagnosed triple-negative breast cancer. * Patient has previously received taxane-based chemotherapy with or without immunotherapy and an antibody-drug conjugate with a topoisomerase inhibitor payload. * Suitable for one of active comparator chemotherapy assessed by investigator. * An archival tumor tissue sample or a fresh tissue sample should be provided. * Life expectancy of ≥ 12 weeks. * Subjects must have measurable disease according to RECIST (version 1.1). * Adequate organ functions. * Sexually active fertile participants, and their partners, must agree to use methods of contraception during the study and at least 6 months after termination of study therapy. Exclusion Criteria: * Preexisting treatment related toxicity Grade ≥ 2 and Grade ≥ 3 immune related adverse reactions. * Preexisting peripheral neuropathy Grade ≥ 2. * Hemoglobin A1C (HbA1c) ≥ 8%. * Has ocular conditions or symptoms that may increase the risk of the study. * History of ILD or pneumotitis, other severe or uncontrolled disease or central nervous system metastases and/or meningeal metastasis. * Previous medication does not meet the requirements. * Known sensitivity to any of the ingredients of the investigational product; History of drug abuse or mental illness. * Documented history of pulmonary embolism or clinically significant cardiac or cerebrovascular diseases . * Active autoimmune disease. * History of another malignancy . * Pleural, abdominal, or pericardial effusion with clinical symptoms or that require drainage treatment. * Not suitable to receive study treatment for other conditions as per investigator.