SBRT, Chemotherapy, and AK112 Neoadjuvant Therapy for Luminal-type Breast Cancer

Inclusion Criteria: This trial aims to enroll patients who treatment-naïve and voluntarily participate and provide written informed consent; Eligible participants must have histologically confirmed and HR+/HER2-negative breast cancer (HER2 immunohistochemistry 0, 1+, or 2+/FISH-); Patients must meet at least one of the following criteria: (1) tumor size \>2 cm, (2) axillary lymph node metastasis, or (3) intent for breast-conserving surgery, but tumor-to-breast volume ratio makes preservation challenging; Additional eligibility requirements include age ≥18 years, an ECOG performance status of 0-1, and baseline laboratory values within acceptable ranges: white blood cell count (WBC) ≥2.0×10⁹/L, absolute neutrophil count (ANC) ≥1.5×10⁹/L, platelet count (PLT) ≥100×10⁹/L, hemoglobin (Hb) ≥90 g/L. Liver function parameters must be within ≤1.5×upper limit of normal (ULN) for total bilirubin (TBIL) and ≤3×ULN for alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Renal function must be preserved, with serum creatinine (Cr) ≤1.5× ULN, or if Cr exceeds this limit, the creatinine clearance rate should be ≥50 mL/min (calculated using the Cockcroft-Gault formula). Coagulation parameters should meet the following thresholds: activated partial thromboplastin time (APTT)≤1.5×ULN and prothrombin time (PT) or international normalized ratio (INR) ≤1.5×ULN. Exclusion Criteria: Received chemotherapy, targeted therapy, or radiotherapy within 12 months before the first dose of the investigational drug, or have undergone solid organ or hematologic transplantation; A history of myocardial infarction or uncontrolled arrhythmias (QTc ≥470 ms by Fridericia's formula) within 6 months before the first dose; NYHA class III-IV heart failure, left ventricular ejection fraction (LVEF) \<50%, or uncontrolled hypertension (systolic BP ≥150 mmHg and/or diastolic BP ≥100 mmHg); Patients with active HIV, tuberculosis, interstitial lung disease, severe pulmonary impairment, or autoimmune diseases requiring systemic immunosuppression will also be excluded; Participants must not have received a live vaccine within 28 days prior to the first dose, though inactivated influenza vaccines are permitted. Patients requiring systemic corticosteroids (\>10 mg/day prednisone equivalent) or immunosuppressants within 14 days before the first dose will be excluded, except for short-term or low-dose corticosteroids, localized applications, and adrenal replacement therapy; Patients with active infections requiring systemic therapy within 14 days prior to enrollment, hepatitis B or C with detectable viral DNA/RNA, history of prior treatment with immune checkpoint inhibitors (anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibodies), participation in another clinical trial within 14 days, major surgery within 4 weeks before the first dose (except for biopsy procedures), severe allergic reactions to monoclonal antibodies or study drug components, pregnancy or lactation, active psychiatric disorders or substance abuse history; Patients who have ceased alcohol consumption may be included. Lastly, investigators may exclude participants based on any other conditions deemed inappropriate for study participation.