NCT + PD1 + Ketogenic Diet and/or Vitamin C for LARC

To explore the efficacy and safety of adding a ketogenic diet and/or high-dose intravenous vitamin C to neoadjuvant short-course radiotherapy followed by mFOLFOX6 chemotherapy combined with serplulimab in patients with locally advanced pMMR/MSS rectal adenocarcinoma through a prospective, randomized, controlled phase II clinical study, providing preliminary evidence for optimizing neoadjuvant treatment strategies for this population.

Inclusion Criteria: 1\. Histologically confirmed rectal adenocarcinoma. 2. Age 18-80 years. 3. Immunohistochemical examination of biopsy specimens indicating proficient mismatch repair (pMMR), or microsatellite-stable (MSS) status. 4\. Clinical stage cT3-T4N0 or cTxN+. 5. The lower margin of the rectal tumor is ≤10 cm from the anal verge. 6. No distant metastases, as confirmed by contrast-enhanced CT of the chest, abdomen, and pelvis and pelvic MRI before treatment. 7\. No evidence of intestinal obstruction, or resolution of obstruction following diverting stoma surgery. 8\. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1. 9. Adequate peripheral blood counts and hepatic and renal function, as defined by the following laboratory values measured within 15 days before treatment initiation: * White blood cell count (WBC) ≥3.0 × 10⁹/L or absolute neutrophil count (ANC) ≥1.5 × 10⁹/L; * Hemoglobin (HGB) ≥80 g/L; * Platelet count (PLT) ≥100 × 10⁹/L; * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \