Brief Summaries Trial Purpose The primary objective of this prospective, randomized, multicenter, open-label, parallel-controlled clinical trial is to evaluate whether intraoperative rectal irrigation during laparoscopic radical resection of low-to-mid rectal cancer reduces postoperative local recurrence rates compared to no irrigation. Secondary objectives include assessing overall survival, incidence of postoperative complications (e.g., anastomotic leakage, stenosis), and quality of life at 6 months (EORTC QLQ-C30 scale).

Participants Will:

• Undergo laparoscopic radical resection with or without rectal irrigation (based on randomization);
• Follow standardized Enhanced Recovery After Surgery (ERAS) protocols postoperatively;
• Attend scheduled follow-ups at 3, 6, 12, 24, 36, and 60 months post-surgery, including clinical evaluations, imaging (CT/MRI), laboratory tests (CEA), and questionnaire assessments;
• Maintain a symptom diary and record rescue inhaler usage (if applicable).

This prospective, multicenter, randomized, open-label, parallel-controlled clinical trial aims to evaluate the efficacy of intraoperative rectal lavage in preventing local recurrence after laparoscopic radical resection for mid-to-low rectal cancer. Despite significant improvements in rectal cancer outcomes through standardized total mesorectal excision (TME) techniques and neoadjuvant therapy, local recurrence remains a serious clinical challenge with poor prognosis. Evidence suggests that exfoliated tumor cells within the bowel lumen may contribute to anastomotic seeding and subsequent local recurrence. Intraoperative manipulation of the tumor and use of circular staplers during anastomosis may further increase the risk of tumor cell dissemination. Rectal lavage represents a potential strategy to eliminate these free intraluminal malignant cells through mechanical flushing and/or cytotoxic effects of lavage solutions.

The study will enroll approximately 1,598 patients (accounting for a 10% dropout rate) across multiple centers in China. Participants must be 18-75 years of age with histologically confirmed adenocarcinoma of the rectum, where the tumor's distal margin is located within 10 cm of the anal verge. All patients must be scheduled to undergo laparoscopic radical resection with sphincter preservation. Key exclusion criteria include history of other malignancies, abdominoperineal resection (Miles procedure) or Hartmann's procedure, emergency surgery for bowel obstruction, severe organ dysfunction contraindicating surgery, pregnancy or lactation, and serious psychiatric disorders.

Eligible participants will be randomly assigned to either the experimental group (rectal lavage with normal saline/povidone-iodine solution) or the control group (no rectal lavage). Both groups will receive standardized laparoscopic TME procedures performed by experienced surgical teams, followed by identical Enhanced Recovery After Surgery (ERAS) protocols. The primary endpoint is the rate of local recurrence. Secondary endpoints include overall survival, incidence of postoperative complications (anastomotic leakage, pelvic infection, wound infection, intra-abdominal hemorrhage, urinary tract infection) graded according to the Clavien-Dindo classification system, and quality of life at 6 months postoperatively assessed using the EORTC QLQ-C30 questionnaire.

Participants will undergo scheduled follow-up assessments at 3, 6, 12, 24, 36, and 60 months after surgery, including clinical evaluations, imaging studies (CT/MRI), laboratory tests (CEA levels), and quality of life questionnaires. The study hypothesizes that the local recurrence rate will be 6% in the rectal lavage group compared to 10% in the control group. With a two-sided alpha of 0.05 and 80% statistical power, this sample size will provide adequate power to detect this clinically significant difference. This investigation will provide high-quality evidence regarding the role of intraoperative rectal lavage in preventing local recurrence after laparoscopic resection of mid-to-low rectal cancer, potentially establishing a simple yet effective intervention to improve oncological outcomes in this patient population.

Inclusion Criteria:

• Age between 18 and 75 years old.
• Pathologically confirmed rectal adenocarcinoma.
• Mid-to-low rectal cancer with the tumor lower margin located ≤10 cm from the anal verge.
• Underwent laparoscopic radical resection for rectal cancer with sphincter preservation.
• Without concomitant multiple primary malignancies.
• Adequate organ function.
• Patients or their family members were able to understand the study protocol, willing to participate in this study, and provided written informed consent.

Exclusion Criteria:

• Concomitant other malignancies or a history of prior malignancies.
• Abdominal perineal resection (Miles' operation) or Hartmann's procedure.
• Failure to open the peritoneal reflection during surgery.
• History of previous pelvic floor surgery.
• Emergency surgery due to bowel obstruction.
• Severe hepatic, renal, cardiopulmonary, or coagulation dysfunction, or other severe comorbidities that render the patient unable to tolerate the procedure.
• History of severe psychiatric disorders.
• Pregnant or lactating women.
• Any other clinical or laboratory conditions considered unsuitable for participation in the trial by the investigators.