Triple attack on aggressive sarcoma: can radiation, immunotherapy, and chemo shrink tumors before surgery?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: Inclusion Criteria: 1. Male or female, aged 18 to 75 years. 2. Histologically confirmed UPS, screened locally and confirmed by central pathology before enrollment. Adequate IHC (at least CK, S100, SOX10, SMA, desmin, MDM2, CDK4) and NGS when feasible (MDM2/CDK4 amplification mandatory) to exclude dedifferentiated liposarcoma and other differentiated tumors. 3. UPS of extremities or trunk. Max diameter \>5 cm, or \<=5 cm with any of: encasement of major neurovascular bundle \>180 degrees; expected limb functional loss \>50% after resection; MDT deems R0 difficult. SBRT-feasible anatomy with \>3 mm margin to critical neurovascular structures or joint. 4. Regional nodes evaluated by imaging (US/CT/MRI/PET-CT). Suspicious nodes (short axis \>=10 mm, abnormal morphology, or high FDG) require pathology. Uninvolved nodes must not be irradiated; involved nodes included with radical dose or resected. 5. Treatment-naive: no prior chemotherapy, targeted therapy, immunotherapy, or local radiotherapy. 6. At least one measurable lesion per RECIST v1.1. 7. ECOG 0-1. 8. Adequate organ function. 9. Signed ICF, good compliance, willing to provide fresh tumor and blood for translational research. Exclusion Criteria: 1. Other malignancy, except completed treatment with no recurrence/metastasis within 2 years. 2. Major surgery within 4 weeks, or systemic steroids (\>10 mg/day prednisone equivalent) or immunosuppressants within 2 weeks. 3. Active infection requiring systemic therapy; active HBV (DNA \>=2000 IU/mL), HCV, syphilis, or HIV positive. 4. Active or relapsing autoimmune disease. 5. Severe comorbidity: NYHA \>=III, ischemic heart disease, uncontrolled hypertension/diabetes; interstitial lung disease or severe pulmonary impairment. 6. Known active brain metastases. 7. Pregnancy/breastfeeding, or refusal of effective contraception. 8. Any investigator-judged risk to safety or completion.