Reducing the Resection Range After Neoadjuvant Therapy for Locally Advanced Upper Rectal and Rectosigmoid Junction Cancers

Inclusion Criteria

• •1. Age 18-80 years.
• •2. Histopathologically confirmed adenocarcinoma of the rectum or rectosigmoid junction.
• •3. Clinical stage cT3-4N+M0, with or without positive mesorectal fascia (MRF), with or without extramural vascular invasion (EMVI); Tumor location confirmed by imaging to be above the peritoneal reflection and by endoscopy to be in the upper rectum or rectosigmoid junction.
• •4. For patients with pMMR (proficient Mismatch Repair; immunohistochemistry shows expression of all four proteins: MSH1, MSH2, MSH6, PMS2) or MSS (Microsatellite Stable) status: Tumor downstaged to T≤3N0M0 after neoadjuvant chemotherapy or total neoadjuvant therapy (TNT). Chemotherapy regimens include, but are not limited to, FOLFOX6, CAPOX, or FOLFOXIRI.
• •5. For patients with dMMR (deficient Mismatch Repair; immunohistochemistry shows loss of expression in two or more of MSH1, MSH2, MSH6, PMS2) or MSI-H (Microsatellite Instability-High) status: Tumor downstaged to T≤3N0M0 after immunotherapy.
• •6. Pre-neoadjuvant therapy / Preoperative staging methods: All patients underwent contrast-enhanced CT for staging. Peri-rectal metastatic lymph nodes: defined as nodes with short-axis diameter ≥10 mm or exhibiting CT characteristics typical of metastasis. Preoperative chest, abdominal CT, and pelvic MRI ruling out distant metastasis.
• •7. No signs of bowel obstruction; OR bowel obstruction that has resolved following proximal diverting colostomy.
• •8. No prior colorectal surgery.
• •9. No prior chemotherapy or radiotherapy.
• •10. No prior treatment with biologic agents (e.g., monoclonal antibodies), immunotherapy (e.g., anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 antibodies), or other investigational drugs.
• •11. Prior endocrine therapy: Allowed.
• •12. Signed informed consent form.