The primary aim is to evaluate the efficacy of neoadjuvant SBRT combined with PD-1 monoclonal antibody and chemotherapy in patients with triple-negative breast cancer, with the endpoint being the pCR rate-defined as the proportion of patients with no residual invasive cancer in the breast and no axillary lymph node metastasis after treatment. This is a single-arm study. Eligible participants will receive : neoadjuvant treatment consisting of SBRT followed by Envafolimab (PD-1 inhibitor), chemotherapy and immunotherapy (Envafolimab). Surgery will be performed after the last chemotherapy cycle. Pathological evaluation will assess the treatment response. Patients will receive adjuvant immunotherapy (Envafolimab) up to 1 year post-surgery.

Inclusion Criteria

Signed written informed consent prior to enrollment

Age ≥ 18 years

ECOG PS score 0-1

Newly diagnosed T1c N1-2 or T2-3 N0-2 breast cancer

Triple-negative breast cancer with PD-L1 CPS < 10

Hemoglobin ≥ 10.0 g/dl, neutrophils ≥ 1.5 × 10⁹/L, platelet count ≥ 100 × 10⁹/L

BUN ≤ 1.5 × upper limit of normal (ULN), creatinine ≤ 1.5 × ULN

Serum bilirubin ≤ 1.5 × ULN, alkaline phosphatase (AKP), AST, and ALT ≤ 2.5 × ULN

Women of childbearing potential must be willing to use contraception during the study

Negative serum or urine pregnancy test within 7 days prior to treatment

Exclusion Criteria

Occult breast cancer

Bilateral breast cancer

Breast tumor unsuitable for SBRT

Unable to undergo MRI scanning

History of other malignancies that may affect survival

Active autoimmune disease or history of autoimmune disease

Current use of immunosuppressants or systemic steroids (within 2 weeks prior to enrollment)

Known allergy to any component of the investigational drugs

Uncontrolled cardiac symptoms or diseases

Active infection or unexplained fever > 38.5°C during screening/before first dose

Other factors likely to cause early study termination (e.g., serious concurrent illnesses, significant lab abnormalities, or social/family circumstances affecting safety/data collection)