The prognosis of recurrent and metastatic triple negative breast cancer (TNBC) is poor, and chemotherapy is still the main treatment for TNBC. Some studies have shown that combination therapy of antibodies targeting cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death-1 (PD-1) significantly improves clinical benefit over PD-1 antibody alone. However, broad application of this combination has been limited by toxicities. Cadonilimab is a humanized immunoglobulin G1 bispecific antibody targeting PD-1 and CTLA-4. It mutates to eliminate Fc receptor and complement-mediated cytotoxic effects. The purpose of this study is to evaluate the efficacy and safety of Cadonilimab combined with chemotherapy as a first or second-line treatment of recurrent and metastatic TNBC. This study is a multicenter, single arm, phase II, non randomized, open label, Simon two-stage design. It is planned to enroll 27 late stage TNBC patients.

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