Unlike benign disease, proctectomy for rectal adenocarcinoma strictly requires total mesorectal excision. Oncologically, adequate resection with a complete mesorectum and negative margins is critical to minimize the chance of local recurrence, with the CRM being a major determinant of overall survival following curative rectal cancer resection. Of critical importance in the early stages of adoption of transanal endoscopic TME for rectal cancer (taTME) was the demonstration of the feasibility of achieving adequate mesorectal dissection and satisfactory short-term oncologic outcomes. The major drive behind increased adoption on this approach has been the suggested improvement in access to the low rectum and mesorectum relative to open and laparoscopic approaches and an enhanced view of dissection planes achieved through the transanal platforms. This bottom-up approach may provide a less obstructed view and manipulation of the perirectal and mesorectal planes, facilitating the mesorectal dissection, especially for low rectal tumors in narrow pelvises.

Since the first published case report of laparoscopic-assisted taTME in 2010 for a mid-rectal T2N1 cancer treated with neoadjuvant therapy [11], at least 12 case series including 247 patients have since published their preliminary perioperative and oncologic results with taTME performed with either open, laparoscopic, robotic, or with no abdominal assistance. Across the 12 published series, 8 % (21/247) of taTME cases were performed as part of an APR, and 92 % as part of sphincter-preserving restorative proctectomy (Tables 11.2 and 11.3).

With respect to tumor selection for taTME , the large majority of studies performed taTME for non-obstructing, resectable tumors including preoperatively staged T1, T2, and T3, N0 or N1 tumors. When studies were performed under protocol [15, 21, 22], and early in their operative experience, most authors specifically excluded T4 and metastatic tumors, local recurrences, and tumors with threatened CRM margins based on staging MRI. Cumulatively, across the 12 published series with sample size ranging from 4 to 56 patients, the mesorectum was complete in 90 % and near complete in 8.7 % of patients, with negative resection margins achieved in 95 %, and an average of 12–33 lymph nodes harvested (Tables 11.2 and 11.3). Although five publications included one to two unsuspected T4 rectal tumors [10, 16, 18, 20, 21], only one study specifically selected unfavorable tumors in male patients for this approach, including large T3 and T4 tumors, located anteriorly, in the distal 5 cm of rectum, and with threatened positive CRM’s [14], all radiated preoperatively. The rationale for this patient selection was to facilitate completion of sphincter-preserving good-quality TME in cases that were otherwise predicted to be technically challenging and associated with a high risk of incomplete mesorectal specimens. The authors were able to achieve a complete mesorectum in every case, but reported a 13 % incidence of positive margins, and 80.5 % overall survival at 24 months, reflecting the advanced stage of the tumors [14].

In the largest and only multicenter taTME series published to date, 56 patients with locally advanced tumors ≤ 5 cm from the anal verge, most of which treated with neoadjuvant treatment (84 %), underwent taTME with laparoscopic assistance with complete or near complete mesorectum achieved in all cases, and a 95 % R0 resection rate [21]. There were three conversions and six cases of delayed anastomosis, no mortality, and a 26 % morbidity rate including anastomotic leakage, pelvic sepsis urinary dysfunction, bleeding, and a cerebrovascular accident. Local recurrence rate at a median follow-up of 29 months was 1.7 %, with 96.4 % overall survival [21].

Although the international experience with taTME is still preliminary with no randomized trial yet comparing taTME with open or laparoscopic TME, two retrospective studies compared outcomes of matched cohorts of patients who underwent taTME vs. laparoscopic TME [19, 20]. Fernandez-Hevia et al. retrospectively case-matched 37 cases of laparoscopic-assisted taTME with 37 cases of laparoscopic TME for rectal cancer and demonstrated no significant differences with respect to quality of the mesorectal specimen, lymph node harvest, resection margins, or intraoperative complications [19]. They also demonstrated comparable 30-day postoperative complications, but a statistically significant lower readmission rate in the taTME group (2 % vs. 6 %) [19]. Velthuis et al. retrospectively matched 25 cases of laparoscopic-assisted taTME with 25 cases of laparoscopic TME, and interestingly, they found that taTME was associated with a significantly higher rate of complete mesorectum than laparoscopic TME (92 % vs. 72 %) [19].

With respect to location, there are no absolute contraindications to performance of the TME, either in part or completely, using a transanal endoscopic approach. As demonstrated in the published series on transanal proctectomy for benign indications, a pure transanal endoscopic approach can be used in completion proctectomy for short rectal stumps. For longer stumps, or when there is concern of possible pelvic adhesions to the proximal stump, transanal procedures are performed with abdominal assistance [13, 23, 24].

With respect to rectal cancer, based on the 12 series of taTME cases published to date, the majority of tumors were located in the mid- and low rectum (<10 cm from the anal verge), with only five studies including high rectal tumors (≥10 cm from the anal verge) [10, 14, 15, 20, 22] (Tables 11.2 and 11.3). Most authors determined that the benefit of using a transanal approach was less evident for upper rectal tumors, where standard laparoscopic techniques can usually achieve adequate TME and sphincter preservation. TME for mid- and low rectal tumors can be performed using a pure transanal endoscopic approach when feasible, or with a hybrid approach with abdominal assistance. Depending on the level of distal rectal or anorectal transection, stapled or handsewn coloanal anastomosis is performed, with or without creation of a colonic J pouch, based on the surgeons’ preference.