• Subjects voluntarily participate in the study, sign the informed consent form (ICF), and are able to comply with study procedures.

• Age ≥18 years and ≤75 years at the time of signing ICF, regardless of gender.

• Histologically confirmed unresectable locally advanced or metastatic bone and soft tissue sarcoma at this institution, including: undifferentiated sarcoma, leiomyosarcoma, myxofibrosarcoma, alveolar soft part sarcoma, pleomorphic undifferentiated sarcoma, chordoma, angiosarcoma, and dedifferentiated liposarcoma.

• For histological subtypes without standard systemic therapy, such as chordoma, prior systemic therapy is not required. Subjects with alveolar soft part sarcoma may be systemic therapy-naïve or have received systemic therapy excluding PD-1/PD-L1 inhibitors.

• For histological subtypes with standard systemic therapy, such as undifferentiated sarcoma, leiomyosarcoma, myxofibrosarcoma, dedifferentiated liposarcoma, and pleomorphic undifferentiated sarcoma, subjects must have received anthracycline-based chemotherapy. Subjects with angiosarcoma must have received paclitaxel- or anthracycline-based chemotherapy, and have developed metastasis or disease progression (≥10% increase in the sum of the longest diameters within 3 months), or be intolerant to standard therapy.

• At least one measurable lesion as assessed by the investigator according to RECIST v1.1.

• Subjects are able to provide tumor tissue samples and blood samples for biomarker testing including PD-L1.

• ECOG performance status of 0-1, with an expected survival ≥12 weeks.

• Clinical laboratory tests at screening must meet the following criteria (no use of blood components, hematopoietic growth factors, leukocyte- or platelet-stimulating agents, or anemia-correcting medications within 14 days before testing):

∙ Hematologic: Absolute neutrophil count (ANC) ≥1.5 × 10⁹/L; Platelet count (PLT) ≥90 × 10⁹/L; Hemoglobin (Hb) ≥90 g/L.

‣ Hepatic function: Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5 × upper limit of normal (ULN); for subjects with liver metastasis, AST and ALT ≤5 × ULN. Total bilirubin (TBIL) ≤1.5 × ULN (subjects with Gilbert syndrome: TBIL \<3 × ULN). Albumin (ALB) ≥30 g/L.

‣ Renal function: Serum creatinine (Cr) ≤1.5 × ULN or creatinine clearance (CCr) ≥50 mL/min (calculated by Cockcroft-Gault formula).

‣ Coagulation: Activated partial thromboplastin time (APTT) ≤1.5 × ULN; International normalized ratio (INR) ≤1.5; Prothrombin time (PT) ≤1.5 × ULN.

‣ Urine protein: Urine protein dipstick ≤1+. If ≥2+, a 24-hour urine protein test is required; subjects with \<1 g/day are eligible.

‣ Cardiac function: Left ventricular ejection fraction (LVEF) ≥50%.

⁃ Female subjects must be non-lactating, and a pregnancy test must be negative before enrollment.

⁃ Subjects of childbearing potential agree to use effective contraception from signing the ICF through at least 180 days after the last dose of study drug.