Rectal cancer is relatively common, with almost 40,000 new cases estimated for 2017 in the US alone. The standard of care for its treatment is total mesorectal excision (TME), the en bloc sharp dissection of the tumor and the mesorectum (the surrounding perirectal lymphatic tissue located within a thin fascial layer) under direct vision. TME has reduced local recurrence rates and improved overall survival. When combined with low anterior resection (LAR), the technique is used to excise tumors in the lower two-thirds of the rectum, a technically challenging surgery due to a narrow pelvis and difficulties in obtaining adequate exposure.

Several surgical techniques are used to perform TME. Dissection using open laparotomy and minimally-invasive laparoscopic or robot-assisted abdominal approaches is performed in a ‘top-down’ manner, where the instruments are inserted transabdominally and the procedure progresses from splenic flexure/sigmoid colon mobilization to rectal resection. A transanal approach may also be used, a ‘bottom-up’ procedure where instruments are inserted through the anus to perform rectal resection and TME. Minimally-invasive laparoscopy can reduce morbidity compared with open laparotomy and has been increasingly used, but high conversion rates from laparoscopy to open surgery have been reported because of technical difficulties in the narrow surgical space. Robotic assistance has the potential to further improve outcomes, including fewer conversions and improved potency compared with laparoscopy, with greater benefits reported in male and obese patients and those undergoing LAR.

However, comparison of open, laparoscopic and robotic approaches is needed, particularly compared with the transanal approach, to help determine which technique may provide optimal outcomes. Inclusion of the most high-risk patients, i.e. those who are most difficult to operate, such as obese patients with narrow pelvis, large mesorectum, large tumor, or bulky prostate, and consideration of oncologic, morbidity, and functional outcomes (i.e. through a co-primary evaluation) should help to achieve this aim. A randomized controlled trial is ethically problematic because of the difficulty in achieving equivalence regarding surgical experience with each technique.

Thus, the prospective, observational rectal surgery evaluation trial (RESET) will aim to study TME with LAR using open laparotomy, laparoscopy, robot-assisted surgery, or transanal surgery in four parallel, case-matched cohorts in centers with expertise in these procedures. The study will be performed in a quality-controlled manner to avoid learning curve concerns while ensuring adequate enrolment for clinical relevance. The primary objective of RESET will be to evaluate each technique in high-surgical-risk, non-metastatic, mid-to-low rectal cancer patients by assessing oncologic, morbidity and functional outcomes in a co-primary endpoint comprising three postoperative measures of success: circumferential resection margin (CRM) ≥1 mm, TME grade III, and minimal postoperative morbidity (absence of Clavien-Dindo grade III-IV complications within 30 days after surgery). Secondary endpoints will also include the co-primary endpoints over the long-term (2 years), as well as quality of surgery, quality of life (QoL), length of hospital stay, operative time and rate of unplanned conversions.