Traditionally, anal preservation surgery is considered only for rectal cancers that are more than 7-8 cm away from the anus, while rectal cancers that are less than 7-8 cm away from the anus are treated by digging out the anal miles. With the improvement of the understanding of the pathology of rectal cancer and the development of surgical techniques, anal preservation surgery is performed for many low rectal cancers that are 5-8 cm away from the anus, and even for early rectal cancers that are 2-5 cm away from the anus. So which rectal cancer patients are suitable for anus-preserving surgery? After rectal cancer is detected, only those who meet 3 conditions are suitable for anal preservation surgery. Such patients are not prone to local recurrence in the pelvis after anal preservation surgery, and the anus can control the exhaustion and defecation well, and the patient’s quality of life is improved. (1) Good anal function: Only preoperative rectal finger examination shows that the patient has good anal contraction function, and such patients can control defecation after anal preservation. Occasionally, elderly and thin patients with poor anal contraction function are not suitable for anal preservation surgery. (2) Good general condition: preoperative CT examination does not reveal extensive distant metastases (such as liver and lung metastases), and patients in good physical condition can only have anal preservation surgery. After the anal preservation surgery, it often takes about 6 months (3-12 months) for the recovery of bowel function to be close to or similar to normal; before recovery, the stool is often frequent or constipated, and frequent stool is more common, sometimes 5 to 10 times a day, which is because the original rectum has been basically removed, and the “new rectum” is in the compensatory period, and patients with poor health need to go to the toilet frequently. This is because after the original rectum has been basically removed, the “new rectum” is in the compensatory period, and patients with poor health need to come and go to the toilet frequently and are not very well fed, so the quality of life of such patients after anal preservation surgery is not improved but decreased. Patients with extensive distant metastases often die soon after their bowel function is restored, before they can fully enjoy the fruits of anal preservation surgery. (3) Relatively good tumor characteristics: Patients with relatively good tumor characteristics are less likely to have local pelvic recurrence after surgery. If local recurrence of pelvic cavity occurs after anal preservation surgery for rectal cancer, it may compress the large intestine in pelvic cavity and cause defecation difficulty or intestinal obstruction, which will have serious impact on patients’ quality of life. Patients with certain activity of tumor should be considered for anal preservation surgery. Tumor activity indicates that the depth of tumor does not exceed the thickness of rectal mesentery and does not infiltrate the pelvic wall. In this way, the resection of the tumor specimen can guarantee a negative annuloplasty margin after resection. Patients with positive cricothyroid margin are prone to local recurrence in the pelvis after surgery and are not suitable for anal preservation surgery. ② Rectal finger examination: to assess the height of tumor location. The complex composed of anal sphincter is called surgical anal canal. Rectal finger examination shows that the distance between the lower edge of the tumor and the upper edge of the surgical anal canal is more than 1 cm (the distance between the lower edge of the tumor and the anal canal is more than 5 cm) before considering the anal preservation surgery. Patients with positive lower tumor margin are prone to anastomotic recurrence after surgery and are not suitable for anus-preserving surgery. ③ Rectal finger examination: to assess the general pathological type of the tumor. Patients to be prepared for anal preservation surgery generally have limited tumor pathology, not “overwhelming” growth, i.e. not diffuse growth, and generally the breadth of the intestinal wall does not exceed 1/2 week, so they are suitable for anal preservation surgery. Such patients are suitable for anus-preserving surgery. Diffuse tumors are highly malignant and have a high rate of local recurrence in the pelvis after surgery, so they are not suitable for anus-preserving surgery. ④ Preoperative biopsy: to determine the histopathological type of tumor. Patients to be prepared for anus-preserving surgery are usually well differentiated rectal adenocarcinoma rather than poorly differentiated mucinous adenocarcinoma or indolent cell carcinoma in terms of histopathological typing. Poorly differentiated mucinous adenocarcinoma or indolent cell carcinoma with high malignancy and high local recurrence in the pelvis after surgery are not suitable for anus-preserving surgery. ⑤ CT or MRI. Pre-operative CT or MRI indicates that the tumor has no obvious external infiltration and no extensive lymph node metastasis in the rectal mesentery, so anus-preserving surgery should be considered. If the tumor has obvious external infiltration and extensive lymph node metastasis, the local recurrence rate of pelvic cavity after surgery is high, so it is not suitable for anal preservation surgery. 6) Under special circumstances, anal preservation surgery via sphincter gap is also feasible for early rectal cancer with small lesions located within the submucosa layer 2-5 cm from the anus. The key factor of whether rectal cancer patients can undergo anal preservation surgery is the pathological type of tumor and the depth of tumor infiltration (rather than the height of tumor location). Assuming a tumor has invaded the pelvic wall, even if the tumor is 8 cm or more from the anus, although the tumor can be removed, this type of surgery is often not radical, and it is better to do an abdominal enterostomy after specimen removal to avoid local recurrence of the tumor compressing the intestinal canal in the pelvic cavity and causing obstruction or difficulty in defecation. If patients with rectal cancer meet the above mentioned indications for anal preservation, laparoscopic double anastomosis, laparoscopic modified Bacon operation, laparoscopic trans-sphincter resection and other anal preservation procedures are feasible according to the situation.