A Prospective, Single-arm, Multicenter Exploratory Clinical Study of Anlotinib Combined With Bempegaldesleukin and Conventional Chemoradiotherapy for the Treatment of Unresectable Locally Advanced or Metastatic Soft Tissue Sarcoma.

Inclusion Criteria:

1. Age: 18 to 80 years.
2. Diagnosis: Pathologically confirmed, investigator-assessed metastatic or unresectable locally advanced soft tissue sarcoma, classified as Stage IV according to the AJCC (8th Edition) staging system. Eligible histologic subtypes per the WHO (2013) classification include anthracycline-insensitive types, primarily: myxoid/round cell liposarcoma, Grade 1 dedifferentiated liposarcoma, clear cell sarcoma, endometrial stromal sarcoma, alveolar soft part sarcoma, extraskeletal myxoid chondrosarcoma, osteosarcoma, chondrosarcoma, Ewing sarcoma/primitive neuroectodermal tumor (PNET), embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, gastrointestinal stromal tumor (GIST), etc. Eligibility of other rare soft tissue sarcoma subtypes will be determined by the investigator.
3. Measurable Disease: At least one measurable or evaluable lesion as defined by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.
4. Life Expectancy: ≥ 3 months.
5. Performance Status: Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
6. Adequate Organ Function: Must meet the following criteria within 7 days prior to treatment initiation:1）Hematological (without transfusion or use of growth factors within 14 days):Hemoglobin (Hb) ≥ 90 g/L,Absolute Neutrophil Count (ANC) ≥1.5 × 10⁹/L,Platelet count (PLT) ≥75×10⁹/L;Biochemical:Total Bilirubin (TBIL) ≤1.5 × Upper Limit of Normal (ULN),Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST)≤ 2.5× ULN,Serum Creatinine (Cr)≤ 1.5 × ULN or Creatinine Clearance (CrCl) ≥ 60 mL/min,Urinalysis: Urine protein\< 2+ and 24-hour urine protein quantification must show protein≤1 g;Coagulation: International Normalized Ratio (INR) and Activated Partial Thromboplastin Time (APTT) ≤ 1.5 × ULN;Cardiac Function: Left Ventricular Ejection Fraction (LVEF) ≥ 50% as assessed by Doppler ultrasound;Thyroid Function: Thyroid-Stimulating Hormone (TSH) ≤ 2.0 × ULN; if abnormal, T3 and T4 levels must be within normal limits for enrollment.
7. Contraception: Women of childbearing potential must have used reliable contraception, have a negative pregnancy test (serum or urine) within 7 days prior to enrollment, and be willing to use adequate contraception during the trial and for 8 weeks after the last dose of the study drug. Men must agree to use adequate contraception or be surgically sterile during the trial and for 8 weeks after the last dose.
8. Treatment Plan and Consent: The investigator plans to administer the combined chemoradiotherapy and targeted immunotherapy regimen, and the patient has provided written informed consent.

Exclusion Criteria:

1. Prior treatment with PD-1/PD-L1/CTLA-4 antibodies, radiotherapy, or any targeted therapy.
2. Tumor invasion of major blood vessels.
3. Active, known, or suspected autoimmune disease.
4. Known history of primary immunodeficiency.
5. History of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation.
6. Pregnant or lactating female patients.
7. Uncontrolled concurrent illnesses, including but not limited to:HIV infection (HIV antibody positive).Active or clinically poorly controlled severe infection.Active hepatitis.Evidence of severe or uncontrolled systemic diseases (e.g., severe psychiatric, neurological, epileptic, or dementia disorders; unstable or decompensated respiratory, cardiovascular, hepatic, or renal diseases; uncontrolled hypertension \[defined as ≥ Grade 2 hypertension per CTCAE despite medical therapy\]).Active bleeding or newly diagnosed thrombotic disease requiring therapeutic anticoagulation, or bleeding tendency; coagulation abnormalities (INR \> 1.5 × ULN, APTT \> 1.5 × ULN).
8. Current participation in another drug clinical trial.
9. Any other condition deemed by the investigator to make the patient unsuitable for inclusion.