The study will evaluate the safety and efficacy of QLC5513 alone or in combination with QL1706 in patients with advanced or metastatic triple-negative breast cancer (TNBC) who had received ≥1 line of prior systematic therapy.

This is a Phase 2, randomized, open-label study. TNBC patients eligible for inclusion will be randomly assigned (1:2) to receive either QLC5513 alone (Arm 1) or QLC5513 plus QL1706 (Arm 2). After the completion or discontinuation of the study treatment, safety follow-up and survival follow-up will be performed. The primary objective is to evaluate the objective response rate (ORR).

Inclusion Criteria:

1. Female aged ≥18 years;
2. TNBC invasive breast cancer confirmed by histology (specific definition: ER <1% positive tumor cells by immunohistochemistry are defined as ER negative, PR <1% positive tumor cells are defined as PR negative, HER2 0-1+ or HER2 ++ but negative by FISH without amplification was defined as HER2 negative);
3. Locally advanced breast cancer (unable to undergo radical local treatment) or recurrent metastatic breast cancer;
4. Progression after at least one prior therapeutic regimens for advanced/metastatic TNBC.
5. At least 1 measurable lesion per Response Evaluation Criteria in Solid Tumors version 1.1.
6. Has protocol-defined adequate bone marrow, renal, hepatic and blood clotting functions.
7. They have not received radiotherapy, molecular targeted therapy, or surgery within 3 weeks before the start of the study, and have recovered from the acute toxicity of previous treatment (if surgery was performed, the wound has healed completely); No peripheral neuropathy or grade I peripheral neurotoxicity;
8. Eastern Cooperative Oncology Group (ECOG) score status 0-1 and life expectancy ≥3 months;
9. Fertile female subjects were required to use a medically approved contraceptive method during the study treatment period and for at least 3 months after the last use of the study drug;
10. Subjects volunteered to join the study, signed informed consent, had good compliance, and cooperated with follow-up.

Exclusion Criteria:

1. Radiotherapy (except for palliative causes), chemotherapy, and immunotherapy were used in the first 3 weeks of treatment, except bisphosphonate (which can be used for bone metastasis);
2. Uncontrolled central nervous system metastases (indicating symptomatic or symptomatic treatment with glucocorticoids or mannitol);
3. A history of clinically important or uncontrolled heart disease, including congestive heart failure, angina pectoris, myocardial infarction, or ventricular arrhythmia within the last 6 months;
4. Persistent grade 1 or higher adverse reactions caused by previous treatments. The exception to this is hair loss or something the researchers don't think should be ruled out. Such cases should be clearly documented in the investigator's notes;
5. Underwent major surgery (except minor outpatient procedures, such as placement of vascular access) within 3 weeks of the first course of trial treatment;
6. Pregnant or lactating patients;
7. Malignancy (except basal cell carcinoma of the skin, which has been cured, and carcinoma in situ of the cervix) in the past 5 years.
8. A prior history of treatment with antibody-drug conjugates (ADCs).