This is a phase 2a clinical trial based on the IDEAL framework to evaluate the safety, feasibility and clinical efficacy of single-port robotic transanal total mesorectal excision (SPr-taTME )surgery. For safety, intraoperative adverse events and 30-day morbidity. For efficacy, successful completion of predefined procedural steps without conversion. The transanal surgical platform consists of a single-port robotic system, while the transabdominal approach can be performed laparoscopically or with single-port robotic assistance.

The study assessed the intraoperative adverse events (device-related and/or procedure-related), postoperative complications, perioperative recovery outcomes, surgical specimen quality, and pathological indices of SPr-taTME in the treatment of mid-to-low rectal cancer.

Inclusion Criteria:

• (1) Mid or low rectal cancer, 0-10 cm from the anal verge (MRI definition); (2) Histological biopsy showing adenocarcinoma; (3) Stage I-III (MRI and abdominal CT), including the downstaged after neoadjuvant therapy; (4) Intention for primary anastomosis; (5) Obtain the informed consent of the patient and his family; (6) Suitable for robotic or laparoscopic surgery. (7) Over 18 years old.

Exclusion Criteria:

1. T3 tumour with margins less than 1 mm to the mesorectal fascia or T4 tumour, determined by MRI-scan (staged after (chemo)radiotherapy if applicable) ;
2. The anal sphincter complex or levator anal muscle is involved;
3. Previous prostate or rectal surgery (excluding local excision) ;
4. Emergency surgery was performed due to complications of a rectal tumor;
5. Malignancy other than adenocarcinoma at histological examination;
6. Pregnancy;
7. Signs of acute intestinal obstruction;
8. Multiple colorectal tumours;
9. Familial Adenomatosis Polyposis Coli (FAP), Hereditary Non-Polyposis Colorectal Cancer (HNPCC), active Crohn's disease or active ulcerative colitis;
10. Planned synchronous abdominal organ resections;
11. Other malignancies in medical history, except adequately treated basocellular carcinoma of the skin or in situ carcinoma of the cervix uteri;
12. Absolute contraindication to general anaesthesia or prolonged pneumoperitoneum, as severe cardiovascular or respiratory disease (ASA class > III)