The goal of this clinical trial is to learn if somatostatin plus a clear liquid diet can help prevent severe leakage after rectal cancer surgery in adults with low or mid rectal cancer who are scheduled to have ultra-low anterior resection. These patients have a higher risk of leakage where the bowel is joined together after surgery.

The main questions it aims to answer are:

Does somatostatin plus a clear liquid diet prevent severe leakage within 1 month after surgery about as well as a prophylactic diverting stoma?

What medical problems, bowel function problems, recovery outcomes, and quality of life outcomes do participants have after surgery and during follow-up?

Researchers will compare somatostatin plus a clear liquid diet without a diverting stoma to prophylactic diverting stoma to see if the somatostatin plus clear liquid diet regimen can provide similar protection against severe leakage while reducing the need for stoma creation.

Participants will:

Have rectal cancer surgery with the bowel joined very close to the anus

Be randomly assigned to receive either somatostatin plus a clear liquid diet for 7 days after surgery without a diverting stoma, or a prophylactic diverting stoma

Have follow-up assessments of leakage, postoperative complications, bowel function, recovery quality, and quality of life

Complete follow-up visits or assessments for up to 3 years after surgery

This is a multicenter, open-label, randomized clinical trial evaluating a postoperative no-stoma management strategy in adults with low or mid rectal cancer undergoing ultra-low anterior resection. Patients undergoing ultra-low colorectal or coloanal anastomosis are at increased risk of anastomotic leakage. A prophylactic diverting stoma is commonly used to reduce the clinical consequences of leakage, but stoma creation may also lead to stoma-related complications, delayed stoma closure, additional surgery, and impaired quality of life.

The study evaluates whether a 7-day postoperative regimen of somatostatin plus a clear liquid diet can serve as an alternative strategy to reduce intestinal contents passing through the anastomosis during the early postoperative period. Somatostatin is used to reduce gastrointestinal secretions, and a clear liquid diet is used to limit solid residue in the digestive tract. The investigational strategy is compared with prophylactic diverting stoma, which is commonly used in patients considered to be at high risk of leakage after low rectal surgery.

Eligible participants will be randomly assigned in a 1:1 ratio to one of two treatment strategies after ultra-low anterior resection. Participants in the experimental group will not undergo prophylactic stoma creation and will receive somatostatin plus a clear liquid diet for 7 days after surgery. Participants in the control group will undergo prophylactic diverting stoma and receive standard postoperative care. Both groups will receive routine perioperative management according to clinical practice at the participating centers.

The primary clinical focus is severe anastomotic leakage within 1 month after surgery, defined as leakage requiring reoperation. The study will also assess postoperative complications, bowel function, quality of recovery, quality of life, and longer-term functional outcomes during follow-up. Participants will be followed for up to 3 years after surgery.

This trial is intended to determine whether somatostatin plus a clear liquid diet without prophylactic stoma can provide similar protection against severe anastomotic leakage compared with prophylactic diverting stoma, while reducing the need for stoma creation and its related burden.

Inclusion Criteria:

1. Adults aged 18 to 75 years
2. Patients with stage I to III rectal malignancy who are scheduled to undergo low anterior resection at a participating gastrointestinal surgery center
3. The lower edge of the tumor is 8 cm or less from the dentate line, or 10 cm or less from the anal verge, based on preoperative colonoscopy, imaging, or digital rectal examination
4. The planned anastomosis is expected to be 2 cm or less from the dentate line, or 4 cm or less from the anal verge
5. Patients have two or more risk factors for anastomotic leakage as assessed by the study team
6. American Society of Anesthesiologists physical status classification is grade 3 or lower
7. Body mass index is less than 30 kg/m²
8. The patient, or the patient's legally authorized representative, is willing and able to provide written informed consent

Exclusion Criteria:

1. Has another colorectal malignant tumor at the same time
2. The final anastomosis after surgery is more than 2 cm from the dentate line, or more than 4 cm from the anal verge
3. Has metastatic disease before surgery
4. Is pregnant
5. Has a mental illness or addictive disorder that would prevent participation in the clinical trial
6. Requires emergency surgery
7. Has inflammatory bowel disease
8. Is allergic to somatostatin or is unable to tolerate somatostatin
9. For participants assigned to the no-stoma group, the surgeon decides that a stoma is required
10. Has received neoadjuvant drug therapy less than 2 weeks before surgery, or radiotherapy less than 8 weeks before surgery
11. Has any other condition that makes it impossible to follow the study protocol

Individual participant data will not be publicly shared because the study involves clinical surgical data and long-term follow-up information from patients with rectal cancer. Data will be stored in a de-identified form for study analysis, but external sharing of individual participant data is not planned under the current ethics approval and informed consent process.

This is an open-label trial. Masking is not feasible because the assigned treatment strategies are clinically apparent: participants either undergo prophylactic diverting stoma creation or do not undergo stoma creation and receive postoperative somatostatin plus a clear liquid diet.