Short-Course Radiotherapy With Tumor-Draining Lymph Node Preservation Followed by PD-1 Inhibitors in pMMR/MSS Stage II-III Rectal Cancer

Inclusion Criteria: * Age 18-75 years old, regardless of sex. * Fibrocolonoscopy or digital rectal examination indicates that the distal border of the lesion is located 5-10 cm from the anal verge. * Pathologically confirmed rectal adenocarcinoma. * Imaging examinations (including pelvic MRI and chest-abdominal CT) confirm a clinical stage of II/III (cT3-T4aN0 or cT2-4aN+, MRF (-), with no distant metastasis) according to the AJCC Cancer Staging Manual, 8th Edition (2018) (for detailed TNM staging of rectal cancer). * If N+, metastatic lymph nodes are confined to the mesorectal and superior rectal artery drainage regions, with no lateral pelvic lymph node metastasis. ⑥ Confirmed by immunohistochemistry or molecular testing to be mismatch repair proficient (pMMR) or microsatellite stable (MSS). ⑦ Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0-1 (see Appendix 2 for details). ⑧ Meeting the following laboratory criteria: Hemoglobin ≥ 90 g/L, white blood cell count ≥ 3.5 × 10⁹/L; Neutrophil count ≥ 1.5 × 10⁹/L, platelet count ≥ 100 × 10⁹/L; Creatinine ≤ 1.0 × upper limit of normal (ULN), blood urea nitrogen (BUN) ≤ 1.0 × ULN; Alanine aminotransferase (ALT) ≤ 1.5 × ULN; Aspartate aminotransferase (AST) ≤ 1.5 × ULN; Alkaline phosphatase (ALP) ≤ 1.5 × ULN; Total bilirubin (TBIL) ≤ 1.5 × ULN; Urine protein negative; normal coagulation time; normal thyroid function. ⑨ Patients with primary rec…