Response-adapted Total Neoadjuvant Therapy Guided by Induction Chemotherapy in Early- and Intermediate-risk Low Rectal Cancer for Implementation of a Watch-and-wait Strategy

Inclusion Criteria12

• Age: 18-80 years; no restriction on sex.
• Histologically confirmed rectal adenocarcinoma with immunohistochemistry and/or genetic testing showing pMMR/MSS status.
• Tumor characteristics assessed by chest-abdominal CT, rectal ultrasound, and MRI meeting all of the following criteria:
• The lower edge of the tumor is ≤5 cm from the anal verge as measured by digital rectal examination or MRI;
• Clinical stage cT1-3abN0-1M0 (for cT1N0, patients suitable for endoscopic resection are excluded);
• MRF (-) (\>1 mm), EMVI (±);
• Negative lateral lymph nodes and \<7 mm in size;
• Maximum tumor length ≤5 cm;
• Tumor circumference involvement ≤2/3.
• After receiving at least two cycles of induction chemotherapy with the XELOX regimen, MRI assessment shows treatment response (tumor length reduced by ≥30% compared with baseline).
• Completion of total neoadjuvant therapy (TNT), including long-course chemoradiotherapy and consolidation chemotherapy (radiotherapy: 25-28 fractions; chemotherapy: 6-8 cycles).
• (For the prospective cohort) Provision of written informed consent for participation in this observational study.