The Optimal Radioimmunotherapy Combinations for Advanced TNBC

Inclusion Criteria:

1. Inoperable locally advanced/metastatic triple-negative breast cancer (defined as ER and PR \<1%; and HER2 negative as IHC 0 or IHC 1+, or IHC 2+ but negative upon fluorescence in situ hybridization (FISH) testing). Patients with ER/PR ≤10% and deemed unsuitable for endocrine therapy by the investigator are also eligible.
2. No prior chemotherapy for advanced/metastatic disease.
3. ECOG PS score of 0 or 1.
4. Presence of 1 to 5 tumor lesions suitable for radiotherapy (individual lesion size between 0.5 and 5 cm, not limited to 1 to 2 organs).
5. At least one measurable lesion outside the radiation field that can be evaluated.
6. Suitable to receive one of the chemotherapy regimens chosen by the investigator: nab-paclitaxel or gemcitabine + carboplatin.
7. Patients with brain metastases are allowed if they do not require local therapy at enrollment or if the metastatic lesion is treated with the assigned radiotherapy regimen.
8. Patients who have previously received PD-1/PD-L1 therapy for early-stage disease are allowed to enroll.
9. Able to provide tumor tissue sections or agree to tumor biopsy during the screening period.
10. Adequate organ and bone marrow function, with specific requirements:

    1. Hematology: Neutrophil count (ANC) ≥1.5×10\^9/L; Platelet count (PLT) ≥90×10\^9/L; Hemoglobin (Hb) ≥90 g/L; No blood product transfusion (including red blood cell and platelet products, etc.) or growth factor (including colony-stimulating factors, interleukins, and erythropoietin, etc.) support treatment within 2 weeks prior to examination.
    2. Liver function: Serum total bilirubin (TBIL) ≤1.5×upper limit of normal (ULN); Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST) ≤2.5×ULN (for patients with liver metastases: ALT and AST ≤5×ULN).
    3. Renal function: Serum creatinine (Cr) ≤1.5×ULN or creatinine clearance \>60 mL/min.

Exclusion Criteria:

1. Received platinum-containing regimens during the adjuvant/neoadjuvant therapy phase, and the interval from the last treatment to recurrence/metastasis is less than 6 months.
2. Have received radiotherapy within 12 weeks prior to enrollment, unless the radiotherapy was for adjuvant purposes and there are lesions outside the previously irradiated field.
3. Extensive tumor metastasis with surrounding normal tissues that cannot tolerate radiotherapy damage.
4. Significant third-space fluid retention (e.g., ascites, pleural effusion, pericardial effusion).
5. Require long-term systemic corticosteroid treatment.
6. Have active autoimmune diseases.
7. Have concurrent severe infections.
8. Other patients deemed unsuitable for enrollment by the investigator.