Surgical resection remains the primary treatment for rectal cancer, but the postoperative incidence of anastomotic leakage (AL) is relatively high. AL not only increases the medical burden on patients, prolongs hospital stays, raises the need for secondary surgery, and elevates perioperative mortality, but also increases the long-term risk of local recurrence and reduces survival rates. There is an urgent need for a simple, effective treatment method that minimizes the burden on patients to prevent anastomotic leakage.

The preoperative placement of a transanal drainage tube (TDT) is believed to effectively drain gas and feces from the intestinal lumen, thereby reducing intestinal pressure and alleviating tension at the anastomotic site, thus preventing AL. Previous studies have shown that traditional drainage tubes cannot effectively prevent leakage. Given the limitations of existing research on traditional TDTs, we plan to use a modified TDT (which allows postoperative irrigation and utilizes a balloon to block feces from adversely affecting the anastomosis) to conduct a randomized, parallel-controlled trial. This study aims to further investigate the role of the modified TDT in preventing and treating anastomotic leakage following rectal surgery

Patients were randomly assigned to two groups: the modified-TDT group and the non-modified-TDT group. Randomization was achieved using a computer-generated random number sequence allocation. To ensure all intraoperative decisions made by the surgeon remained unaffected by group assignment, surgeon allocation concealment was implemented : Surgeons were only informed of the group assignment and implemented the intervention according to the randomization result after completing the intestinal anastomosis and deciding whether to create a diverting stoma (DS) during the surgery. All surgical procedures strictly adhered to the guidelines for the diagnosis and treatment of colorectal cancer and the principles of total mesorectal excision (TME). Preservation of the left colic artery (LCA) was determined by the surgeon based on their experience and assessment of the patient's condition. Upon completion of the anastomosis, the surgeon decided on DS construction based on an assessment of risk factors for anastomotic leakage (AL). Pelvic drainage was utilized in all cases in this study.

Inclusion Criteria:

• Rectal adenocarcinoma (confirmed by pathology);
• Tumor location: The lower edge is ≤10 cm from the anal verge;
• Age: ≥18 and ≤80 years old;
• ASA ≤3 ;
• After assessment, laparoscopic/robotic sphincter - preserving surgery for rectal cancer is feasible;
• T2 - 4N0 - 3M0~T0 - 1N1 - 3M0 & non- local recurrence;
• Signed informed consent form;
• Able to understand the risks of participating in the trial.

Exclusion Criteria:

• Emergency surgery;
• Presence of multiple primary colorectal cancers;
• History of long - term use of immunosuppressants or corticosteroids;
• Patients with severe mental illness or uncontrolled infection before surgery;
• Pregnant or breastfeeding women;
• Bowel obstruction before surgery.