Laparoscopic natural orifice specimen extraction surgery (NOSES) for low rectal cancer has a good minimally invasive effect. However, the NOSES prognosis studies are all small sample retrospective studies. This study conducted a multicenter prospective randomized controlled trial of NOSES surgery for low rectal cancer to compare the difference in surgical outcomes between conventional laparoscopic surgery and NOSES surgery for low rectal cancer. A total of 500 patients were planned to be enrolled, including 250 in the control group and 250 in the experimental group. The primary end point was 2-year disease-free survival (DFS), and the secondary end points were surgical safety, postoperative pathology, postoperative defecation, urination, and sexual function. Through a large sample size study, this study aims to clarify the advantages of NOSE surgery for low rectal cancer, promote the promotion of low rectal cancer NOSES surgery in the country, standardize the way of low rectal cancer NOSES surgery, improve the surgical treatment of patients with low rectal cancer, improve the quality of life of patients, reduce the burden of patients, and increase the satisfaction. And improve the international influence of the project team in the field of minimally invasive surgical treatment of colorectal cancer.

Research Objectives:

1. To compare the difference in the oncological effect between laparoscopic radical resection of low rectal cancer with anal specimens (NOSES I type) and laparoscopic assisted surgery for low rectal cancer;
2. To compare the safety of laparoscopic radical resection of low rectal cancer with anal specimens (NOSES I type) and laparoscopic assisted surgery for low rectal cancer within 30 days of perioperative period;
3. To explore the difference in the prophylactic stoma implementation and the positive rate of tumor cells in pelvic flushing fluid between laparoscopic radical resection of low rectal cancer with anal specimens (NOSES I) and laparoscopic assisted resection of lower rectal cancer.

Primary end Point: 2-year Disease-free survival (DFS) Secondary end points :(1) incidence of SSI; (2) Incidence of serious postoperative complications (anastomotic leakage, postoperative bleeding, etc.); (3) R0 removal rate; (4) Postoperative recovery (pain, exhaust and defecation time, eating time, postoperative hospital stay, etc.); (5) Postoperative pathological conditions (distance between upper and lower margins, number of lymph nodes, circumferential margins, etc.); (6) 2-year RFS and OS.

Exploratory end points :(1) prophylactic colostomy rate; (2) Positive rate of tumor cells in pelvic flushing fluid.

Inclusion criteria:

1. Patients aged 18-75 years;
2. Adenocarcinoma confirmed by pathology;
3. colonoscopy or imaging examination confirmed that the distance between the lower edge of the tumor and the anal edge was less than 5cm;
4. Preoperative imaging diagnosis was CT1-3NXM0;
5. Preoperative colonoscopy or imaging diagnosis confirmed that the maximum diameter of the tumor was not more than 5cm;
6. Body Mass Index (BMI)≤30kg/m2;
7. No local complications (no obstruction, incomplete obstruction, massive active bleeding, no perforation) Formation of pores and abscesses without invasion of adjacent organs);
8. The hematopoietic functions of heart, lung, liver, kidney and bone marrow meet the requirements of surgery and anesthesia;
9. Voluntarily sign the informed consent form.

Exclusion criteria:

1. Preoperative evaluation of lateral lymph node metastasis;
2. Previous history of malignant tumor;
3. Simultaneous multiple primary colorectal cancer;
4. Patients with contraindications of laparoscopic surgery, such as severe cardiopulmonary insufficiency;
5. Previous multiple abdominal and pelvic surgeries or extensive abdominal adhesions;
6. Patients with intestinal obstruction, intestinal perforation, intestinal bleeding, etc., requiring emergency surgery;
7. Patients with familial adenomatous polyposis, Lynch syndrome associated rectal cancer, and active inflammatory bowel disease;
8. have a history of serious mental illness;
9. pregnant or lactating women;
10. Patients with uncontrolled infection before operation;
11. The investigator did not consider the patient to be eligible for the trial.

Exit Criteria:

1. Patients with distant metastasis confirmed by intraoperative exploration or postoperative pathology, including liver, pelvic cavity, ovary, peritoneum, distant lymph node metastasis, etc.;
2. Intraoperative exploration was necessary for combined organ resection;
3. After enrollment in the study, patients requiring emergency surgical resection due to intestinal obstruction, intestinal perforation, intestinal bleeding, etc.
4. Patients who requested to withdraw from the study cohort for various reasons after enrollment;
5. Those who fail to complete the institute planning for various reasons after being enrolled in the study.

Inclusion Criteria:

1. Patients were aged between 18 and 75 years;
2. Pathologically confirmed as adenocarcinoma;
3. Colonoscopy or imaging examination confirmed that the distance between the lower edge of the tumor and the anal margin was ≤ 5cm;
4. Preoperative imaging diagnosis was ct1-3nxm0;
5. Preoperative colonoscopy or imaging diagnosis confirmed that the maximum diameter of the tumor was not more than 5cm;
6. Body mass index (BMI) ≤ 30kg / m2;
7. No local complications (no obstruction, incomplete obstruction, no massive active bleeding, no puncture Formation of pores and abscesses without invasion of adjacent organs);
8. The hematopoietic functions of heart, lung, liver, kidney and bone marrow meet the requirements of surgery and anesthesia;
9. Voluntary informed consent.

Exclusion Criteria:

1. Preoperative evaluation of patients with lateral lymph node metastasis;
2. Previous history of malignant tumor;
3. Simultaneous multiple primary colorectal cancer was diagnosed;
4. There are contraindications to laparoscopic surgery, such as severe cardiopulmonary insufficiency;
5. Patients who had undergone abdominal and pelvic surgery for many times or had extensive abdominal adhesions;
6. Patients with intestinal obstruction, intestinal perforation, intestinal hemorrhage and other emergency operations;
7. Patients with familial adenomatous polyposis, Lynch syndrome associated rectal cancer, and inflammatory bowel disease in the active phase;
8. Have a history of serious mental illness;
9. Pregnant or lactating women;
10. Patients with uncontrolled infection before operation;
11. The investigator considered that the patient should not participate in the trial.