Until recently, the utilization of TES has remained largely confined to high-volume and specialized centers. For several decades, widespread adoption of TEM and TEO was hindered by prohibitively high costs of the rigid platforms, scarcity of training, and steep learning curve associated with mastering of techniques. In 2009, during the height of enthusiasm for single-incision laparoscopy , an alternate transanal endoscopic setup using single-incision laparoscopic disposable ports was described named transanal minimally invasive surgery (TAMIS) [11, 12]. TAMIS has rapidly broadened adoption and application of TES for a variety of indications without compromising the benefits of TEM or TEO. Because TAMIS ports are not anchored to the operating table, it requires the operating surgeon to work side by side with an assistant who holds the bariatric length laparoscope that is recommended for use during these cases. TAMIS can be performed using standard laparoscopic equipment through a variety of single-incision platforms at much lower per-case costs relative to the cost of capital investment in rigid platforms and specialized TEM/TEO equipment [7]. Several commercially available devices have been described for TAMIS, but in the USA, the commercially available devices include the SILS Port (Medtronic, Mansfield, MA, USA) and the GelPOINT Path Transanal Access Platform (Applied Medical, Rancho Santa Margarita, CA, USA, Fig. 22.1c). The Triport (Olympus, Center Valley, PA) and the SSL (single-site laparoscopic access system , Ethicon Endo-Surgery, Cincinnati, OH, USA) have been reported in small series with comparable results mostly outside the USA [13, 14]. Flexible laparoscopes such as the Endoeye Flex (Olympus) and standard colonoscopes have been used through TAMIS platforms in order to reach higher up in the rectum and overcome the instrument collision. Interestingly, the use of automated suturing devices and self-retained barbed sutures , as well as specialized high flow insufflation and smoke evacuation systems to maintain a stable pneumorectum and a clear surgical field, has increased the per-case costs of TAMIS. High-flow CO₂ insufflation units such as the UHI-4 (intra-abdominal Insufflation Unit, Olympus) and the Airseal Insufflation System (SurgiQuestInc, Milford, CT, USA) have been used in conjunction with TES platforms. The Airseal in particular provides a continuous flow circuit that evacuates CO₂ and smoke and quickly recirculates filtered and high-pressure CO₂, thereby maintaining a stable pneumorectum at all times. The Airseal insufflation system is reminiscent of the TEM automatic pressure-controlled CO₂ insufflation system, but it requires the use of disposable specialized cannulas inserted through the transanal platform. Finally, the use of TAMIS has also been described in conjunction with robotic platforms , harnessing the advantage of magnified 3D optics and greater dexterity of the robotic EndoWrist movements [15].

While the use of conventional laparoscopic equipment with TAMIS can be versatile and cost-saving, it poses significant limitations as well. The maneuverability of straight instruments through a small transanal workspace remains limited, and overcoming instrument collision makes for a steep learning curve in TAMIS [16]. In addition, the shorter TAMIS platforms provide limited access to the proximal rectum, and rectal lesions located behind haustral valves in upper rectum may be more difficult to reach, resect, and rectal defects more difficult to close using TAMIS platforms relative to the longer TEM or TEO platform [17]. The longer rigid platforms facilitate successful transanal closure of these defects by maintaining patency of the rectal lumen, particularly in the event of leakage of CO₂ following peritoneal entry. This is reflected in the relatively low conversion rates to laparoscopy or laparotomy in large TEM and TEO series which range from 0 to 41.6%, but average 10% [4, 5]. On the other hand, peritoneal entry during TAMIS appears to result in high rates of conversion to laparoscopic closure of rectal defects, ranging from 0 to 86%, which likely reflects the difficulties stenting the rectum adequately enough to permit closure of the rectal defects [18–20].

Recent improvements in the treatment of rectal cancer can be attributed to the standardization of TME technique and the selective use of chemotherapy and radiation therapy [21]. Local recurrence rates have decreased from as high as 45% using traditional techniques to <10% after TME alone, and <6% after TME if performed with negative circumferential radial (CRM) and distal margins , in conjunction with radiation therapy [22, 23]. The introduction of minimally invasive techniques including laparoscopy and robotics has not altered the morbidity or negative impact of open TME on quality of life following sphincter-sparing and non-sphincter sparing TME . Among the largest randomized controlled trials comparing open versus laparoscopic TME such as the COLOR II, ACOSOG, and COREAN trials, wound infection rates have ranged from 5 to 6.5% and anastomotic leaks from 1.2 to 10%, without statistically significant differences between the groups [24–26]. Oncologic equivalence or non-inferiority of laparoscopic TME was demonstrated across all the above trials except for the ACOSOG Z6051and AlaCart trials [24, 27]. The 30–40% incidence of sexual, urinary, and defecatory dysfunction are compounded by the addition of neoadjuvant radiation and have not been lowered with the use of laparoscopic or robotic surgery, despite improved visualization of pelvic nerves during pelvic dissection [25, 26]. However laparoscopic TME is significantly more technically challenging and is associated with a steep learning curve. Laparoscopic TME is particularly challenging during dissection of the lowermost part of the mesorectum, especially in male patients with high body mass index (BMI) and narrow pelvis. While conversion rates have progressively decreased from 30% early on in the laparoscopic TME experience to 16% and 11% in the COLOR II and ACOSOG Z6051 trials, respectively [24, 25, 28], overall adoption of laparoscopic TME has remained at 30% or less.

The recent increase adoption of robotic surgery during TME reflects the superior 3D visualization and enhanced dexterity and ergonomics provided by the da Vinci™ system (Intuitive Surgical, Sunnyvale, CA, USA), which may help overcome some of the challenges of deep pelvic dissection and reduce the steep learning curve [29]. Despite the suggestion that robotic surgery may reduce conversion rate during TME across several large-case series and comparative studies, the recent ROLARR trial, a prospective, randomized-controlled of robotic-assisted versus laparoscopic TME, has not shown any statistically significant difference in conversion rates or other perioperative outcomes between laparoscopic and robotic TME [30].

In light of the ongoing anatomic and technical challenges of achieving sphincter-preserving TME while achieving a complete mesorectal specimen and negative margins, the concept of transanal Natural Orifice Transluminal Endoscopic Surgery (NOTES) colorectal surgery rapidly evolved from the experimental setting to clinical application [31, 32]. By accessing the rectum and mesorectum from a primarily transanal endoscopic approach, taTME aims to overcome these limitations and facilitate completion of these complex procedures. Since the report of the first case of hybrid laparoscopic-assisted transanal TME in a female patient with a T2 N1 mid-rectal cancer in 2009 using a TEO platform, several small pilot studies subsequently demonstrated the feasibility and safety of this approach [33–35]. These pilot studies were quickly followed by medium-sized series of taTME with the largest cohort size ranging from 16 to 140 patients with taTME performed for benign and malignant indications, in combination with LAR or APR , using a variety of transanal platforms and types of transabdominal assistance (open, multiport, single port and hand-assisted laparoscopy, and robotic). Cumulatively, the series have reported 98% rate of complete and near-complete TME specimens and a CRM-positive CRM ranging 0–13%, which is comparable to historical open and laparoscopic TME outcomes with the benefit of exceedingly low conversion rates

Although the experience with taTME remains preliminary with no long-term oncologic or functional outcomes and no randomized trials, these preliminary results strongly support taTME as an attractive alternative and potential new standard in the surgical treatment of resectable low and mid-rectal cancer.

TEM was initially intended for the management of large adenomas deemed unresectable by standard polypectomy or conventional transanal excision (TAE ) . Since its inception, TES has become an attractive alternative to standard LAR and APR with data supporting its safety profile, significantly lower postoperative pain, and reduced recovery time [36, 37]. Most importantly, TES provides a much more suitable choice for benign lesions that would otherwise be overtreated with LAR or APR . Indications for local excision using TES have expanded to include large adenomas, incompletely resected adenomas with high-grade dysplasia, small low-risk carcinoids, other benign rectal pathologies, as well as carefully selected T1 rectal tumors and more advanced rectal tumors in the palliative setting.

The use of TES alone in the curative treatment of rectal cancer remains controversial. Although earlier TEM cohort studies demonstrated unacceptably high rates of LR for unselected T1 (range, 0–26%) relative to a ≤6% LR rate for T1 tumors treated with radical proctectomy [55], more contemporary series have demonstrated its curative potential for carefully selected T1 rectal cancers with low-risk histopathological features [56]. The risk of locoregional recurrence following local excision of T1 rectal cancer is directly correlated to the risk of associated lymph node metastasis , which is not addressed by any of the local excision techniques. While standard preoperative staging of rectal cancer with CEA , stating CT scans and pelvic MRI and/or endorectal ultrasound (ERUS ) can exclude patients with T2 and more advanced rectal tumors, the challenge resides in selecting T1 tumors associated with the lowest risk of lymph node metastasis and that will likely be cured with R0 local resection alone.

Histopathologic factors associated with increased risk for local recurrence following local excision of T1 rectal tumors include depth of submucosal involvement, poor differentiation grade, lymphovascular invasion (LVI) , positive resection margins (R1 resection), large tumor size, and the presence of tumor budding [57–59]. One of the most important independent predictor for local recurrence following local excision of T1 rectal cancer is the extent of submucosal invasion. In a longitudinal cohort study of 182 patients with adenocarcinoma, Kikuchi et al. determined that the level of tumor invasion into the submucosa is predictive of LR following TEM for T1 tumors. Submucosal invasion was further classified as sm1, sm2, and sm3 representing invasion into the upper, middle, and deepest third, respectively, with deeper submucosal invasion correlating with increased risk of LVI and lymph node metastasis [60]. Kikuchi and Nascimbeni independently determined from large cohorts of T1 colorectal cancers undergoing radical resection that sm1, sm2, and sm3 depth of tumor invasion was associated with a 0–3%, 8–10%, and 23–25% risk of lymph node metastasis, respectively [59, 60]. As a result, local excision alone for sm3 and high-risk sm2 lesions is associated with higher risk of lymph node metastasis and local recurrence.

Another adverse prognostic factor associated with local recurrence and metastases , as well as significantly worse overall and disease-free survival in colorectal cancer, is the presence of tumor budding [55, 61, 62]. Tumor budding refers to the presence of single malignant cells or a small clusters of tumor cells (less than 5 cells) at the invasive tumor margin [63]. Ueno et al. demonstrated that in T1 colorectal carcinoma, high tumor grade, LVI, and tumor budding are all independently associated with lymph node metastases. Patients without any of these three features showed low rates of lymph node metastases (1%, 1/138); in the presence of one risk factor, the rate of nodal metastases increased to 21% (12/58), and when two or three factors were present, the risk was 36% (20/55), suggesting that local excision with TEM with negative resection margins would be sufficient treatment for early T1 colorectal carcinoma [64].

Based on the National Comprehensive Cancer Network (NCCN) guidelines , indications for transanal excision of rectal cancer include T1 tumors less than 3 cm in size, with no radiographic evidence of lymphovascular or perineural invasion. Unfavorable histopathologic features include &gt;3 cm in size, LVI, positive margin, or sm3 depth of tumor invasion (Table 22.2).

As described earlier, while LR rates following local excision of unselected T1 rectal cancer were reported to range from 0 to 26%, these outcomes from older series reflected the heterogeneity of cohorts with respect to the type of local excision (TAE or TEM, submucosal dissection or full-thickness), variations in preoperative tumor staging, completeness of resection (R0 or R1, en bloc or fragmented), treatment with neoadjuvant or adjuvant therapy, tumor size, and detailed histopathologic analysis to stratify outcomes based on risk for occult nodal disease [65, 66]. This is contrast to more contemporary TES for T1 rectal cancer series that have demonstrated that with careful preoperative staging and risk stratification based on detailed histopathologic review, local recurrence following TES rates range from 0 to 10%, which is in line with oncologic outcomes from radical proctectomy [67, 68].

It has been established in previous studies that local excision alone with TEM and TEO for T2 and more invasive rectal cancers with curative intent results in unacceptably high rates of LR [67]. Across early TEM series, the reported LR rates for T2 tumors not treated with neoadjuvant therapy ranged from 20 to as high as 36%, reflecting the associated high incidence of lymph node metastasis [69, 70]. In a systematic comparison of TEM versus radical resection with TME for T1 and T2 rectal tumors of performed by Mellgren et al., the 5-year LR rate for T2 tumors was 47% versus 6% after radical resection (p = 0.001). While there was no statistical difference in the overall 5-year survival between local resection and radical surgery groups for T1 tumors (72% versus 80%, p = 0.5), there was a statistical difference for patients with T2 tumors (65% versus 81%, p = 0.03) [69].

Although the standard of care for locally invasive rectal cancer remains radical surgery with TME, there has been an increasing trend towards organ preservation based on evidence that clinically staged T2 and T3 rectal tumors downstaged with neoadjuvant chemoradiation therapy (CRT) may be cured with local excision or observation alone. Several small retrospective cohorts of patients with locally invasive rectal tumors treated primarily with CRT because they either declined radical surgery or were deemed poor surgical candidates demonstrated acceptable long-term oncologic data. A small randomized trial comparing preoperative CRT followed by TEM alone versus laparoscopic TME in patients with T2 rectal tumors found no difference in overall survival between the two groups (72% in CRT + TEM versus 80% in laparoscopic TME, p = 0.609). LR rates were also similar between the groups (12% with TEM versus 10% with TME, p = 0.686) [71]. With improvement in preoperative staging and more intensive chemoradiation regimens therapy, complete pathologic response rates greater than 20% have been documented with sustained good local control using either local excision or observation alone. The recent prospective multicenter ACOSOG Z6041 phase II trial reported the 3-year oncologic outcomes in 72 T2N0 tumors located in the distal 8 cm of the rectum, treated with capecitabine, oxaliplatin, and 54 Gy of radiation followed by local excision using TAE or TES [72]. The 3-year DFS for the intention-to-treat group was 88.2% and 86.9% for the per-protocol group. Overall, organ preservation could be achieved in 66% of patients, and the authors concluded that neoadjuvant therapy followed by local excision should be reserved for those with clinically staged T2N0 lesions that are not otherwise amenable to TME [72].

Most recently, advocates of organ-preserving strategies have investigated the outcomes of nonoperative management for rectal tumors that have demonstrated complete clinical regression following neoadjuvant therapy. The Habr-Gama group has the largest clinical experience to date with the “watch-and-wait” approach for locally advanced rectal cancer. Their findings in a cohort of 70 patients with preoperatively staged T2–T4, N0–N2 tumors treated with intensive CRT regimens demonstrated a 68% rate of complete clinical response based on reevaluation with imaging, endoscopy, and digital rectal examination (DRE) 10–12 weeks later to confirm the absence of residual tumor or other mucosal irregularity [73]. These 47 patients were subsequently observed, and a sustained complete clinical response was observed in 51% of the entire cohort at 3 years follow-up. The remaining 49% with evidence of recurrent disease underwent immediate or salvage surgery with either TEM or radical surgery. Based on these data, although the possibility of definitive, nonsurgical treatment of rectal cancer with CRT alone remains limited to a subset of biologically responsive tumors, advances in neoadjuvant chemoradiation therapy may potentially spare 50% of patients with T2 rectal tumors from radical surgery. Several European series have corroborated the findings from the Habr-Gama group [74, 75] and demonstrated that with more aggressive CRT regimens, the rates of complete clinical response can exceed the historical 20–30% rate, although this may be at the cost of increase toxicity, possible overtreatment of early rectal tumors, and delayed local recurrence that may not be surgically salvageable.

TES has also been demonstrated to be effective at treating a variety of other rectal tumors and benign conditions. Local resection using TES has been well established in the management of low-risk rectal carcinoid tumors, particularly when incompletely resected endoscopically. In the absence of histopathological risk factors for lymph node metastasis including size ≤10 mm and absence of LVI, and early stage confirmed by ERUS and CT scans, rectal carcinoids are amenable to local excision [76]. TES may be better suited than EMR, ESD, and TAE for definitive treatment of rectal carcinoids due to the ability to perform full-thickness rectal excision. Two large series on rectal carcinoids treated with TEM either as initial modality or for completion of incomplete endoscopic excision included 24 and 27 patients, respectively, with lesion size ranging from 7.5 to 10.1 mm and located within 9 cm from the anal verge (AV). These studies demonstrated a 100% R0 resection rate with 100% OS and DFS at a 30–70.6 months follow-up [77, 78]. TES has also been described in small case series of carefully selected GIST tumors and benign retrorectal tumors including tail gut cysts and rectal duplication cysts tumors, as a minimally invasive alternative to transcoccygeal resection or radical proctectomy [79, 80]. There have also been a number of recent case reports and case series on the successful use of TES in the management of complex benign conditions such as recurrent rectourethral [81], rectovesical [82], and rectovaginal fistulas [83] that had failed traditional repair. In addition, other miscellaneous use of a transanal endoscopic approach has included strictureplasty and transanal repair of colorectal anastomotic complications including leaks and abscesses [39]. Finally, TES can be used for palliation of bleeding rectal tumors in patients who are medically unfit to undergo other palliative procedures including fecal diversion, stenting, surgical debulking, cryosurgery, embolization, and palliative radiation [84].

Historically, a relative contraindication for TES included rectal lesions located higher than 8–10 cm from the AV, particularly if anterior, due to the high chance of full-thickness excision resulting in peritoneal entry. That is because peritoneal entry during full-thickness TEM excision was previously considered to be a complication requiring immediate conversion to laparotomy with low anterior resection or fecal diversion in order to mitigate the risk of leak and infection [85]. However, recent publications from experienced centers have demonstrated the feasibility and safety of transanal suture closure of upper rectal full-thickness defects without increased morbidity or adverse oncologic outcomes [86–88]. Based on this experience, it is generally recommended that only lesions within the reach of the 12–20 cm rigid proctoscope, and otherwise amenable to local excision, should be considered for full-thickness TES resection.

At the other extreme end of the rectum, due to their design and location in the anal canal following deployment, TAMIS does not permit access to rectal polyps located within 4 cm of the AV [16]. For lesions partially or entirely located within the distal 4 cm of the anorectal canal, the TEM and TEO platforms can often be pulled back maximally to permit exposure without losing excessive pneumorectum. This is in contrast to TAMIS where resection must be combined with a standard TAE approach for the distal part of the dissection.

With respect to rectal tumor size, nearly obstructing, near-circumferential, and circumferential tumors constitute a contraindication for TES. This is due to the anticipated difficulty in achieving R0 resection and safely closing giant rectal defects using a purely transanal approach, without resulting in rectal stenosis or incomplete closure [89].

With respect to patient safety, TES can be safely performed in the large majority of patients, including high-risk surgical patients, provided they are acceptable candidates for general anesthesia. TES can also be safely performed in patients with morbid obesity (BMI ranging from 35 to 66) as reported in a recent case series, without an increase in adverse events [90, 91].

Although firm consensus is building that sphincter-preserving LAR for low rectal tumors is the sweet spot for transanal TME, any type of proctectomy, including completion proctectomy , total proctocolectomy , APR , extralevator abdominoperineal excision (ELAPE) , restorative proctectomy , or proctocolectomy (RPC) with ileoanal J pouch (IPAA ) reconstruction, can be performed using taTME for a variety of benign and malignant etiologies. Based on the preliminary procedural, perioperative, and short-term oncologic data published to date, specific indications and contraindications of taTME with respect to specific pathology and anatomic factors have been described.