The purpose of this study was to evaluate the efficacy and safety of Cadonilimab monotherapy in the treatment of patients with advanced soft tissue sarcoma who have received at least one chemotherapy (including anthracyclines) for advanced diseases (excluding alveolar soft part sarcoma).

After being informed about the study and potential risks, all patients giving written informed consent will undergo a screening period (≤28 days) to determine eligibility for study entry. At week 0, patients who meet the eligibility requirements will be treated with Cadonilimab monotherapy.

Inclusion Criteria:

• 1. Written and signed informed consent.
• 2. Male or female, age≥ 18 and ≤ 70 years old on day of signing informed consent.
• 3. Pathologically confirmed unresectable or metastatic soft tissue sarcoma, mainly including Undifferentiated pleomorphic sarcoma/malignant fiber histiocytoma, Alveolar soft part sarcoma, dedifferentiated liposarcoma, fibrosarcoma, Leiomyosarcoma, Anigosarcoma, Synovial sarcoma.
• 4. Patients who have failed at least one chemotherapy (including anthracyclines) in the last 6 months (excluding acinar soft tissue sarcoma).

Exclusion Criteria:

• 1. Prior use of investigational products or devices within 4 weeks prior to the first administration of the study treatment.
• 2. Concurrent enrollment into another clinical study, except the study belongs to investigational, non-interventional studies or the follow-up period of interventional studies.
• 3. Prior exposure to any experimental antitumor vaccines, or any agent targeting T-cell costimulation or immune checkpoint pathways (eg, anti-PD-1, anti-PD-L1, anti-CTLA-4, anti-CD137 or anti-OX40 antibody, etc).
• 4. Active autoimmune diseases;
• 5. History of transplantation;
• 6. Known history of primary immunodeficiency virus infection or known history of testing positive for human immunodeficiency virus (HIV).