Inclusion Criteria:

• Recurrent or metastatic TNBC patients;
• TNBC defined by immunohistochemistry as ER<1%, PR<1%, Her2=0~1+, or 2+ while HER2 Fish test shows no amplification；
• Previous received no or only first line chemotherapy treatment for recurrent or metastatic TNBC；When the time between cancer metastasis and the end of adjuvant chemotherapy exceeds 1 year, the systemic chemotherapy for metastasis treatment is recorded as first-line treatment; When less than 1year, the systemic chemotherapy for metastasis treatment is recorded as second-line treatment；
• ages 18 to 75 years at the time of signing the informed consent form (ICF);
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 or 1;
• expected survival of ≥3 months; at least one measurable lesion per RECIST (version1.1);
• acceptable renal and liver function;

Exclusion Criteria:

• They had received ICIs (i.e., anti-PD-1 antibodies, anti-PD-L1 antibodies, and anti-CTLA-4 antibodies.)；
• Patients with active central nervous system (CNS) metastatic lesions or meningeal metastases；
• Patients with an active autoimmune disease that requires systemic treatment in the past two years；
• A known history of primary immunodeficiency；
• Pregnant or lactating women；
• Previous or current abnormalities of any disease, treatment, laboratory tests may confuse the study results, affect the subject's participation in the study