This study sets up the final study end point and three detailed goals as the following.

The main objective of study: This trial is done to assess the safety and benefit of robotic resection compared with conventional laparoscopy-assisted resection for curative treatment of patients with cancer of the mid or low rectum.

Detailed goal of study:

The primary endpoint: This study is designed to assess whether robotic surgical system improves the quality of rectal cancer surgery, especially in total mesorectal excision quality and a circumferential margin positivity rate

The secondary endpoint: This study aims to compare 3- and 5-year disease-free survival and overall survival after robot and laparoscopic resection of distal rectal cancer. This study will also assess the pelvic autonomic nerve preservation, short-term morbidity, pathological quality (i.e. number of harvested lymph node), local recurrence, and blood loss during surgery.

Recently, the efficacy and oncological safety of laparoscopy has been demonstrated for treating colon cancer, and similar long-term results at 5-year confirmed by the several multicenter study trial. However, conventional laparoscopic surgery for rectal cancer is technically more difficult than colonic resection because of the confined space in the pelvis and the limitations of existing laparoscopic instruments which have a restricted range of movement compared with the provided by the surgeon's hand. Consequently, recent studies which compared short-term outcomes between open and laparoscopic rectal resections have reported higher rates of conversion to open surgery, positive circumferential margins, and increased anastomotic leakage in patients who underwent laparoscopic approach.

The da Vinci® Surgical System (Intuitive surgical, Sunnyvale, CA, USA) was introduced as the next advance in minimally invasive surgery to overcome the technical limitations of laparoscopy. The advantages of robotic assistance include enhanced dexterity, improved three-dimensional vision, and more intuitive instrument manipulation. This device eases the technical challenges of the minimally invasive approach and may make a complex surgical task more accessible to surgeons without extensive laparoscopic experience.

With its dependence on precise dissection in a narrow pelvic cavity, it is anticipated that rectal cancer surgery is one of the indications most likely to benefit from robot assistance. However, it is difficult to conclude whether robot assistance leads to better outcomes because few studies have directly compared the three existing techniques. Although robotic rectal excision has been reported to be safe and feasible in the recent literatures, a number of these results were based on small number of case series. There have been no randomized trials demonstrating the safety of robotic surgery in the treatment of rectal cancer. This study is designed to assess the efficacy and safety of robotic surgery compared with that of laparoscopic surgery for mid or low rectal cancer.

Inclusion Criteria:

• Eligibility rule of enrollment
• Rectal adenocarcinoma that were 10 cm or less from the anal verge
• at least 18 years old & at most 80 years old
• Clinically diagnosed cT3N0-2 disease
• Clinical diagnosis of carcinoma involving a single rectal segment
• Patients with adequate hepatic, renal, and bone marrow function, and a left ventricular ejection fraction of 55% or higher measured by echocardiography

Exclusion Criteria:

• The presence of metastasis to the liver, lung, brain, bone, abdominal aortic lymph node, lateral pelvic wall lymph node and inguinal lymph node
• A past history of the cancer occurring in other body areas than the rectal cancer (except for a past history of the radical resection due to skin cancer)
• Severe cardiac diseases or failure
• Severe pulmonary diseases or dysfunction
• The presence of psychiatric diseases
• The concurrent presence of other severe medical diseases
• An ineligibility to participate in the clinical study based on the judgment of investigators from a legal perspective