Background: Laparoscopic assisted right hemicolectomy is recommended for right colon cancer. As a more minimally invasive procedure, intracorporeal ileocolic anastomosis has potential advantages: reducing torsion and traction on the mesentery, reducing skin incision length and enhancing postoperative recovery. However, the longer operative time, greater risk of intra-abdominal infection and steep learning curve for intestinal anastomosis performed under laparoscopic conditions, does this increase the incidence of postoperative complications, especially the incidence of anastomotic leakage, and whether it affects There is no high-level research evidence on the survival of patients.

Study design: COlOR IV study is an international prospective, multicenter, randomized controlled clinical study of intraperitoneal anastomosis versus extraperitoneal anastomosis after laparoscopic right hemicolectomy for colon cancer . The study will include a quality assessment phase before randomisation to ensure required competency level and uniformity of the intracorporeal and extracoporeal techniques.

Endpoint: Primary outcome is anastomotic leakage within 30 days after surgery. Main secondary endpoint is 3-year disease-free survival rate. Secondary endpoints are mortality and morbidity, postoperative recovery, overall survival, surgical specimen quality, quality of life.

Statistics: The primary endpoint is anastomotic leakage within 30 days after surgery. The anastomotic leakage rate was set to 2% in the both groups, and an increase in the incidence of anastomotic leakage of 2.5% was considered inferior. The one-sided significance level was 0.025, the power was 0.9. The dropout rate was 20%, and taking into account the post-randomization analysis (dropout 5%), the total sample size was 1158. There were 579 cases in the intracorporeal anastomosis group and 579 cases in the extracorporeal anastomosis group.

Main selection: Patients with histologically proven right colon cancer (cecum, ascending colon and proximal 1/3 of the transverse colon malignant tumor), clinically stage I-III, and intention for right hemicolectomy with primary anastomosis.

Hypothesis: The hypothesis is that intracoporeal anastomosis will have comparable anastomotic leak rate and 3-year DFS, but faster postoperative recovery with extracoporeal anastomosis.

Inclusion criteria

1. Age: 18 ~ 80 years, male or female;
2. Histological or cytological diagnosis of right colon cancer (cecum, ascending colon and proximal 1/3 of the transverse colon cancer);
3. Stage I-III according to the AJCC-TNM classification including downstaged tumor based on adequate imaging of the thorax and abdomen;
4. Intention for right hemicolectomy (including extended right hemicolectomy) with primary anastomosis;
5. Informed consent according to local requirements Exclusion criteria

1) T4b tumor determined by CT scan; 2) Malignancy other than adenocarcinoma at histological examination ; 3)Other malignancies in medical history, except adequately treated basocellular carcinoma of the skin or in situ carcinoma of the cervix uteri; 4) Previous history of colorectal cancer or synchronous multiple colorectal malignancies; 5) Complications requiring emergency surgery (obstruction, perforation, etc); 6) Planned synchronous abdominal organ resections; 7) Pregnant or lactating women; 8) Familial Adenomatosis Polyposis Coli (FAP), active Crohn's disease or active ulcerative colitis; 9) Absolute contraindication to general anesthesia or laparoscopic surgery.

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