Exploratory Study of Short-Course Radiotherapy Followed by Adebrelimab Combined With Chemotherapy for Organ Preservation in Locally Advanced Rectal Cancer

This prospective, single-arm, exploratory clinical study aims to evaluate the efficacy and safety of short-course radiotherapy (SCRT) sequentially followed by adebrelimab combined with chemotherapy as an organ-preservation strategy in patients with locally advanced resectable rectal cancer. Approximately 155 eligible patients will be enrolled after providing full written informed consent and passing screening, and will receive SCRT followed by adebrelimab plus chemotherapy. The primary efficacy endpoint is the complete response (CR) rate assessed at the end of Cycle 4 or Cycle 8 of treatment. Efficacy evaluation will be conducted after 4 cycles of treatment, and subsequent treatment regimens will be determined according to each patient's condition.

Inclusion Criteria: * 1\. Age 18-75 years, of either sex; * 2\. Stage II/III disease (cT3-T4N0 or cT2-4N+, without distant metastasis, per the 8th edition of the AJCC Cancer Staging Manual, 2018) as assessed by magnetic resonance imaging (MRI) or endoscopic ultrasound (EUS); * 3\. The lower border of the lesion located ≤10 cm from the anal verge, as assessed by fiberoptic colonoscopy or digital rectal examination; * 4\. Histologically confirmed or centrally reviewed rectal adenocarcinoma; * 5\. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1; * 6\. Hematologic and biochemical parameters meeting the following criteria within 7 days prior to enrollment: 1. Hemoglobin ≥90 g/L; absolute neutrophil count (ANC) ≥1.5×10⁹/L; white blood cell count (WBC) ≥3.5×10⁹/L; platelet count ≥100×10⁹/L (patients must not have received blood transfusion or growth factor support within 14 days prior to blood sample collection); 2. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5× the upper limit of normal (ULN); alkaline phosphatase (ALP) ≤2.5× ULN; 3. Serum total bilirubin \