During the past three years, a revolutionized radical surgical approach for rectal cancer ("down to up TME " approach or "transanal TME (TaTME)"approach, which is opposite to the conventional approach) has emerged and it is a concept that combines natural orifice transluminal endoscopic surgery(NOTES) and total mesorectal excision(TME) with curative intent. The feasibility, safety and reproducibility of it were first demonstrated in swine survival experiments and subsequently in human cadaver series, and then it was successfully applied to human patients in few centers around the world, most of which were performed with assistance of laparoscopy, namely hybrid transanal TME. In addition, pure-NOTES without conventional laparoscopic assistance (no scar) has also been demonstrated, though the cases were more limited. In the initial stage, our group has successfully performed this no-scar transanal TME in a series of human cadavers with satisfactory outcome. Hence the investigators conduct this study, looking to see if this pure transanal NOTES investigational procedure is a safe and effective approach to radically remove rectal cancer of the mid and lower rectum and meanwhile, if it can reduce pain, gain faster recovery and better function and life quality when gaining the best cosmetic effect.

Transanal total mesorectal excision (TaTME) is a novel development in the field of colorectal surgery which combines the mini-invasive concept of natural orifice transluminal endoscopic surgery(NOTES), the technique of single-port laparoscopic surgery and the principle of total mesorectal excision with curative intent for treating rectal cancer. Based on the platform of either transanal endoscopic microsurgery(TEM) or transanal minimally invasive surgery (TAMIS), it is an innovative way of retrograde TME dissection from bottom to up with or without laparoscopic assistance. It is supposed to facilitate distal rectal mobilization, thus achieving precise and sufficient distal margin and to reduced need for multiple stapler firings in transecting the rectum, consequently decreasing anastomotic leakage rates which is especially important for obese male patients with a narrow pelvis where exposure to the distal rectum from the abdominal approach can prove difficult. It could also protect neurovascular bundle with better visualization and exposure and has the advantage of better function and avoiding sacrificing sphincter. After a series of preclinical trail of animal and cadaver, it has been successfully applied to humans and successional reports have proved its feasibility and safety. However, the majority of published series is hybrid NOTES, which need the assistance of conventional laparoscopic surgery from above to bottom and abdominal incision, scar, pain and incision related complications such as wound infection, abscess, hernia and implanted incisional tumors cannot be necessary avoided. It is also worried that the cost will increased since two groups of surgical equipment are needed(the abdominal and perineal) and more surgical staff are required if the two team operate at the same time(two-team approach). Up to date, as far as we have known, the pure transanal TME NOTES without any laparoscopic assistance has also been successfully performed in human patients though the cases are rare. The investigators of our center have also successfully performed pure-NOTES rectal resection in human cadavers in the past few months, and are confident to move this forward to conduct this pilot study to evaluate the feasibility and safety of this surgery in rectal cancer patients.

Inclusion Criteria:

• Biopsy-proven adenocarcinoma of the rectum
• No previous abdominal surgery, no distant metastasis or synchronous colon cancer
• BMI≤ 35kg/m2
• Clinical staging (T1 or T2 or T3) with N1-2M0
• Patients of rectal adenocarcinoma with T3N0 or N (+) received preoperative concurrent chemoradiotherapy (CCRT) as neoadjuvant therapy
• Rectal cancer located 4-12 cm from the anal verge
• The diameter of primary tumor should <6cm
• Patients must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• American Society of Anesthesiology (ASA) classⅠ to Ⅲ lesions
• After the evaluation of Multi-disciplinary team (MDT)
• Written informed consent

Exclusion Criteria:

• T4 tumor that invade the external sphincter or levator ani muscle or neighbor organs
• Recurrent rectal cancer
• Distant metastasis
• Obstructing rectal cancer
• Synchronous colon cancer
• Pregnant or breast-feeding women
• Fecal incontinence
• History of prior colorectal cancer
• History of inflammatory bowel disease
• Other malignancies diagnosed within the previous year
• Mental illness
• Any evidence of active infection
• History of bleeding diathesis or coagulopathy
• Impaired renal or hepatic function that could not tolerate surgery