The goal of this observational study is to explore the safety and feasibility of laparoscopic intracorporeal anastomosis in colorectal cancer surgery. The main questions it aims to answer are: 1. If intracorporeal anastomosis is safe in terms of short-term outcome? 2. If intracorporeal anastomosis can achieve the same oncological outcome as conventional extracorporeal anastomosis?

This study is a retrospective real-world research initiated by the Chinese Academy of Medical Sciences Cancer Hospital, including Cancer Hospital of the Chinese Academy of Medical Sciences, Shenzhen Hospital and Peking University First Hospital. The study aims to retrospectively analyze the clinical data of approximately 2,000 patients who underwent laparoscopic surgery with preoperative imaging staging of cT1-4aNanyM0 and pathological diagnosis of adenocarcinoma or high-grade intraepithelial neoplasia from April 2016 to April 2020. The patients will be divided into the intracorporeal anastomosis group (IA) and extracorporeal anastomosis group (EA) based on the surgical records. The primary endpoints of the study are 3-year disease-free survival (DFS) and 3-year overall survival (OS). The secondary endpoints include overall complication rate within 30 days, postoperative pain score, time to first flatus after surgery, time to first bowel movement after surgery, time to first oral intake after surgery, length of hospital stay, and postoperative quality of life.

Inclusion Criteria:

1. Patients voluntarily enrolled in this study and signed an informed consent form;
2. Age: 18-75 years;
3. Completion of colonoscopy and biopsy, with pathological confirmation of adenocarcinoma or high-grade intraepithelial neoplasia;
4. Preoperative enhanced CT or MRI examination showing no evidence of distant metastasis;
5. Preoperative staging as cT1-3NanyM0;
6. Underwent laparoscopic surgery.

Exclusion Criteria:

1. Contraindications to laparoscopic surgery;
2. Cases requiring emergency surgery due to acute bowel obstruction, perforation, or bleeding;
3. Patients with distant metastasis;
4. Patients with multiple primary colorectal cancers;
5. Patients with a history of malignancy;
6. Patients unwilling to sign the informed consent or unwilling to follow the study protocol for follow-up.

Patients underwent laparoscopic colorectal surgery with intracorporeal or extracorporeal anastomosis