Minimally invasive transanal excision for rectal tumors: technical feasibility compared to conventional approach

Ji Yeon Mun; Gyu Sung Geong; Nina Yoo; Hyung Jin Kim; Hyeon-Min Cho; Bong-Hyeon Kye

doi:10.3393/ac.2024.00864.0123

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Original Article Minimally invasive surgery Minimally invasive transanal excision for rectal tumors: technical feasibility compared to conventional approach: Ji Yeon Mun¹, Gyu Sung Geong¹, Nina Yoo¹, Hyung Jin Kim², Hyeon-Min Cho¹, Bong-Hyeon Kye¹; Annals of Coloproctology 2025;41(2):162-168.
DOI: https://doi.org/10.3393/ac.2024.00864.0123
Published online: April 29, 2025

¹Department of Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Suwon, Korea

²Department of Surgery, Eunpyeong St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

Correspondence to: Bong-Hyeon Kye, MD, PhD Department of Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, 93 Jungbu-daero, Paldal-gu, Suwon 16247, Korea Email: ggbong@catholic.ac.kr

• Received: November 26, 2024 • Revised: January 12, 2025 • Accepted: January 19, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
Graphical abstract
INTRODUCTION
METHODS
RESULTS
DISCUSSION
ARTICLE INFORMATION
SUPPLEMENTARY MATERIALS
REFERENCES

Abstract

Purpose
The technique for transanal resection of rectal tumors has evolved from conventional methods to minimally invasive approaches. However, the research comparing long-term results between these approaches is limited.
Methods
Between 2016 and 2022, a total of 133 patients who underwent transanal excision were analyzed. Patients were classified into 2 groups according to surgical approach: conventional transanal approach (CTA) and minimally invasive transanal approach (MTA). Medical records were analyzed to compare surgical and oncological outcomes between the 2 groups.
Results
There were no significant differences observed in patient’s demographics and tumor characteristics, except the MTA group exhibited a statistically longer distance from the anal verge. Although statistical significance was not reached, the MTA group demonstrated a 100% margin-negative rate in contrast to the CTA group, which had worse outcomes for both margin status and fragmentation. Recurrence was observed only in the CTA group containing pT1 rectal cancer and grade 1 neuroendocrine tumor, with negative margins and no fragmentation.
Conclusion
The minimally invasive approach did not demonstrate statistical superiority but showed technical feasibility through the absence of margin-positive cases and the use of the clip handle method. Further studies are needed to validate these findings and assess broader applicability.
Keywords: Transanal endoscopic surgery; Natural orifice endoscopic surgery; Transanal endoscopic microsurgery

Graphical abstract

INTRODUCTION

Since the introduction of transanal excision (TAE), it has replaced radical rectal resection for benign rectal lesions or early rectal cancer [1]. Consequently, it significantly reduces the complications from the radical rectal surgery such as anastomosis leakage, urinary/fecal dysfunction, and ostomy formation that may occur after radical resection [2–4]. The conventional TAE opens the narrow rectum using rectal retracting instrument to secure space, uses a long open surgical instrument to confirm the tumor, secures margins, and then performs full-thickness excision. However, the narrow and long anal canal limits visibility, and there are restrictions on the range of movement, making it difficult to access rectal masses located proximally.

To overcome these limitations, transanal endoscopic microsurgery (TEM) or transanal endoscopic operation (TEO) method were developed by introducing endoscopic devices into TAE [5, 6]. Both TEM and TEO utilize a rigid, long, cylindrical device equipped with a rectoscope, which is fixed to the operation table. While the installation and operation of both techniques are quite similar, a key difference lies in the visualization method: TEM involves the surgeon looking directly through the built-in binocular stereoscopic rectoscope, whereas TEO connects the rectoscope to a monitor, allowing the surgeon to operate while viewing the procedure on screen. Both TEM and TEO provide a magnified field of view compared to the naked eye and facilitate access to more proximal rectal lesions through the long instruments [7, 8]. Some studies TEM and TEO showed superior oncologic outcomes than conventional TAE due to reduced tumor fragmentation and a higher rate of the negative margin status [9]. However, TEM and TEO have the drawback of being bulky, making attachment and detachment cumbersome, and requiring their own equipment.

The most recently developed transanal minimally invasive surgery (TAMIS) introduced a single-port laparoscopic platform for TAE. Unlike TEM/TEO, TAMIS allows the use of a single-port laparoscopic system and familiar laparoscopic instruments [10]. Recently, the TAMIS technique has been widely adopted in a minimally invasive TAE approaches.

Research results for long-term follow-up on transanal excision are limited, and while there are some comparative studies between TAE and TEM/TEO [7, 9] or TEM/TEO and TAMIS [11], there is scarce research comparing the minimal invasive transanal approach including TEM/TEO and TAMIS with conventional TAE. Therefore, based on the surgical outcomes of TAE performed at our institution over 6 years, we aim to compare both surgical and oncological results.

METHODS

Ethics statement

This study was approved by the Institutional Review Board of St. Vincent’s Hospital (No. VC24RISI0015). The need for informed consent was waived due to the retrospective nature of the study.

Study design and patients

This is a retrospective study at a single institute. The study population included all patients who underwent TAE for rectal mass from January 2016 to December 2022. Patients were divided into 2 groups according to the surgical approach: conventional transanal approach (CTA) group and minimally invasive transanal approach (MTA) group.

Surgical indication

The study targeted rectal tumors located between the dentate line and the rectosigmoid junction that could not be resected via colonoscopy. A transanal approach was performed when it was considered feasible to achieve a pathologic T0 state through resection and to close the rectal wall in a full-thickness manner after tumor removal. Therefore, TAE was only performed when the tumor's base did not exceed 40% of the rectal circumference [12]. If the tumor's base satisfied this criterion, the tumor size was not restricted unless it interfered with the surgical field or the manipulation of instruments during the procedure.

The criteria for tumor height were applied equally to both benign and malignant tumors. In the CTA group, tumors located within 10 cm from the anal verge (AV) were included, while in the MTA group, the indication for tumor height could be extended to the rectosigmoid junction if the surgical field and instrument manipulation were not compromised.

Meanwhile, in cases where adenocarcinoma was confirmed on biopsy, the indication was restricted according to the National Comprehensive Cancer Network (NCCN) guidelines [13]: tumors occupying less than 30% of the rectal circumference and measuring 3 cm or smaller in size, clinically Tis or T1 stage, exhibiting well to moderately differentiated features, with absence of lymphatic, vascular, or perineural invasion, and showing no evidence of nodal involvement or distant metastasis in preoperative image evaluation, were eligible for transanal resection.

In the NCCN guidelines, only rectal cancer located within 8 cm of the AV was selected as the target of the local excision [13]. So, surgeons applied the NCCN guideline's indication of height of the tumor in patients with the CTA group. However, in the MTA group, if the tumor was located below the rectosigmoid junction and could be sufficiently reached through the minimally invasive transanal approach, the indication for tumor height was extended to include tumors located proximal to 8 cm from the AV.

Preoperative evaluation

Preoperative evaluations were performed for all patients who required transanal surgery for rectal tumors. The location of the tumor and the degree of lumen occupation were assessed through previous colonoscopy images, and a digital rectal examination was performed to evaluate the tumor's height and mobility. When the colonoscopic biopsy evaluated the tumor as benign, preoperative imaging studies, including rectal sonography and abdominopelvic computed tomography (CT) were performed. On the other hand, if the colonoscopic biopsy confirmed a malignant tumor, the clinical T and N categories of the primary tumor were assessed using rectal magnetic resonance imaging, and abdominopelvic and chest CT scans were performed to evaluate distant metastasis (clinical M category). Additionally, preoperative blood tests included carcinoembryonic antigen measurements to determine the baseline carcinoembryonic antigen level.

Surgical approach

In patients who are scheduled for TAE, Surgeons performed colonoscopy the day before surgery to confirm the tumor direction and place hemoclips in the peritumoral lesion. These peritumoral hemoclips serve as a handle to facilitate retraction.

On the day of surgery, after general anesthesia, a jack-knife or lithotomy position was performed depending on the location of the tumor. After securing the space by retracting the anus, the surgeon checked the hemoclips and rectal lesion. After marking the circumferential margin 1 cm from the tumor with a bovie, the surgeon grasped the hemoclip to retract the rectal lesion and performed full-thickness resection. Finally, the surgeon performed primary closure using barbed suture material.

In the MTA group, surgical procedure is the same as that of the CTA group, except for using a TEO flatform or single-port trocar and laparoscopic instruments. For TEO, TEO rectoscope and instruments (TEO, 24292TK/OK, Storz) were used. For TAMIS, all single-port trocars that can be mounted on the anus are applicable. At our institution, we utilized 2 single-port trocars (Glove Port, 431-AT, Nelis; New Port, KSILS-2PB, EROP), while other instruments and cameras were the same as those used in laparoscopic abdominal surgery. To maintain a stable pneumorectum, CO₂ pressure was set at 12 mmHg, and the flow rate was set at 20 L/min.

Outcome

The primary outcome of this study is the rate of en bloc resection with negative margin, which is defined as a complete resection of the tumor without fragmentation and with a negative resection margin. The resection margin was considered positive if tumor cell components were found within 1 mm of the circumferential resection margin or the perimeter, in the pathological review. Tumor fragmentation was defined as a gross finding indicating that a tumor mass had been divided into 2 or more separate tumors. Recurrence rate and postoperative complication rate were analyzed as secondary outcomes.

Statistical analysis

Statistical analysis was performed using the IBM SPSS ver. 29.0 (IBM Corp). Student t-test was used for continuous data, and Fisher exact test was used to compare categorical data. For continuous data showing an abnormal distribution, the Mann-Whitney U-test was performed. The results are presented as mean values and standard deviations for continuous normally distributed variables, as mean ranks for continuous abnormally distributed variables, and as counts and percentages for categorical data.

RESULTS

A total of 133 patients who underwent TAE included in this study. Among them, 98 patients (73.7%) underwent conventional TAE (CTA group). Eight patients who underwent TEO and 27 patients who underwent TAMIS were assigned to the MTA group (35 patients, 26.3%). We compared the patient’s demographics and pathological data between the CTA and MTA groups. There was no significant difference in age, body mass index, and American Society of Anesthesiologists (ASA) physical status between the 2 groups (Table 1).

We also compared tumor characteristics between the 2 groups (Table 1). There was no significant difference in tumor size, and the same results were seen when comparing benign and malignant tumors separately. However, there was a significant difference in tumor location. The distance from the AV was statistically longer in the MTA group than CTA group. In the tumor pathology, overall, neuroendocrine tumor (NET) occupied the most indication, followed by adenoma and adenocarcinoma. There was no significant difference in the proportion of pathology in each group, except in the CTA group, where 6 pT1 and 2 pT2 adenocarcinomas were included. These 2 pT2 tumors, clinically confirmed to be T1 before surgery, were pathologically determined to be pT2 after surgery. Each of these two patients underwent either additional surgery (low anterior resection) or radiation therapy.

Table 2 shows the surgical outcomes of the CTA and MTA groups. The overall lateral margin-negative rate was 92.9% in the CTA and 100% in the MTA group (P=0.305). All margin-positive specimens belonged to the CTA group. Also, the MTA group showed no deep margin positivity, while the CTA group showed 3 deep margin-positive specimens. The same results were seen when analyzing benign and malignant tumors separately (Supplementary Tables 1, 2). Tumor fragmentation also occurred more frequently in the CTA group than in the MTA group. However, no statistical difference in margin status and fragmentation was observed (7.1% vs. 2.9%, P=0.360). Notably, the primary outcome, en bloc resection without fragmentation rate, showed a tendency to be higher in the MTA group, although statistical significance was not achieved (85.7% vs. 97.1%, P=0.067).

The overall postoperative complication rate was 9.02% and there was no difference in the complication rate between 2 groups. The urinary difficulty was most common complication in the CTA group, while the postoperative fever was common in the MTA group (Table 3, Supplementary Tables 3, 4).

Two patients experienced recurrence, both of whom were included in CTA group. One of them was diagnosed with pT1 rectal cancer and the other was diagnosed with NET grade 1. Both patients had margin-negative results (Table 4). There was no statistically significant difference between the two groups.

DISCUSSION

The aim of our study was to compare the surgical outcome between the conventional transanal and MTA for rectal tumor. Ever since Parks and Stuart [1] performed the first TAE, the application of TAE has expanded beyond benign tumors to include early rectal cancer, Tis or T1 [4, 14]. However, the field of view and movement of the instrument is limited due to narrow and long anal canal. Therefore, new approach was introduced using the minimally invasive instrument. The laparoscopic light source and scope allow a wide view in a narrow anal canal, and the long laparoscopic instrument allows access to more proximal lesion. Meanwhile, there was little study on whether benefit of the MTA led to better surgical outcomes compared to conventional TAE. Therefore, we divided patients who underwent TAE into the conventional approach group (CTA group) and the minimally invasive approach group (MTA group) and compared the results.

In this study, tumor size was not different between the 2 groups, but the distance from the AV was significantly higher in the MTA group than in the CTA group. This result is probably due to the long length of the laparoscopic instrument and wide view, facilitating access to proximal lesions. Furthermore, distal rectal tumor can also be resected by minimally invasive approaches. In a current study, tumor location of MTA group was ranged from 3 to 13 cm. In particular, the TAMIS approach has the advantage that the single-port device can be easily mounted and removed. Therefore, surgeons can easily perform full-thickness sutures with the naked eye after removing the single port when full-thickness sutures using laparoscopic instruments is difficult. In conclusion, TAMIS approach has the benefit of taking advantage of the laparoscopic device during dissection and simultaneously using the conventional method when necessary.

There was no significant difference in the en bloc resection without fragmentation rate, which was the primary outcome of this study, between the 2 groups. Similarly, neither the margin-negative rate nor the tumor fragmentation rate showed any significant differences when analyzed separately between the groups. However, the fact that there was not a single margin-positive rate in the MTA group, and the CTA group consistently shows a worse outcome in both margin status and fragmentation. In the recent meta-analysis, which compared conventional TAE and TEM, TEM showed higher margin-negative rate, reduced rate of specimen fragmentation than convention transanal excision [15].

We analyzed why MTA groups showed no margin involvement. First the surgeon could clearly make the demarcation 1 cm from the tumor under a broad surgical view, especially the proximal lesion. In addition, the clip placed with a colonoscopy before surgery served as a handle. By utilizing the clip as a handle, proper traction can be achieved, thereby securing sufficient margin from the tumor, and enabling margin-negative surgery (Fig. 1). Additionally, employing this method is advantageous in achieving the principles of non-touch technique in cancer surgery, as there is no need to directly manipulate or handle the tumor. The same clipping method was used in the CTA group. However, the usefulness was lower than that of the MTA group because the clip could not be gripped adequately due to the limited visibility. Additional research is needed to verify the usefulness of clipping.

In this study, 2 recurrences were confirmed in the CTA, whereas none were found in the MTA group. The patients who relapsed were diagnosed with pT1 rectal cancer and grade 1 NET, respectively, and the margin of specimens were all negative, and there was no tumor fragmentation. One patient received adjuvant concurrent chemoradiation therapy after refusing radical surgery, and the other received low anterior resection. Although no recurrence was found in the MTA group, no statistical difference in recurrence rate was found between the 2 groups. Two patients had no high-risk factor, and specimens were not margin-positive or fragmented. Regarding the cause of the recurrence, we assumed that it was because the tumor was located in the lower rectum, which increases the risk of local recurrence based on its anatomical position [16, 17].

This study has several limitations. First, this study has an inherent bias due to its retrospective and nonrandomized design. Particularly, there was a difference in tumor location between the 2 groups, which could potentially influence recurrence, making it challenging to evaluate oncologic outcomes in this study. Additionally, the small sample size limits the statistical interpretation and the ability to draw robust conclusions. Finally, there were limitations in deriving results because not all marginal information was obtained in all patients. However, this study is meaningful in that it provides a comparison of surgical outcomes between conventional TAE and minimally invasive TAE (especially TAMIS), which has yet to be extensively studied using long-term data.

In conclusion, the minimally invasive approach did not demonstrate statistical superiority in this study. However, the absence of margin-positive cases in the MTA group and the introduction of the clip handle method highlights the technical feasibility of the minimally invasive approach. Further prospective, randomized, and large-scale studies are required to validate these findings and explore the broader applicability of this approach.

ARTICLE INFORMATION

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Acknowledgments

The authors thank all participating patients and those who set up the cancer databases.

Author contributions

Conceptualization: JYM, NY, HJK, BHK; Data curation: JYM, GSG; Formal analysis: JYM, GSG, NY, BHK, HMC; Investigation: JYM, GSG; Methodology: JYM, NY, HJK, BHK; Supervision: NY, HJK, BHK; Validation: NY, HJK, BHK; Writing–original draft: JYM; Writing–review & editing: all authors. All authors read and approved the final manuscript.

SUPPLEMENTARY MATERIALS

Supplementary Table 1.

Benign tumor surgical outcome

ac-2024-00864-0123-Supplementary-Table-1.pdf

Supplementary Table 2.

Malignant tumor surgical outcome

ac-2024-00864-0123-Supplementary-Table-2.pdf

Supplementary Table 3.

Benign tumor complication

ac-2024-00864-0123-Supplementary-Table-3.pdf

Supplementary Table 4.

Malignant tumor complication

ac-2024-00864-0123-Supplementary-Table-4.pdf

Supplementary materials are available from https://doi.org/10.3393/ac.2024.00864.0123.

Fig. 1.

Intraoperative images of the transanal minimally invasive surgery (TAMIS) surgical procedure. (A) Marking around the tumor with bovie. (B) Appropriate traction using the hemoclip as a handle. (C) Complete full-thickness excision was performed.

Table 1.

Demographic and clinical characteristics of patients undergoing transanal excision (n=133)

Characteristic	CTA group (n=98)	MTA group (n=35)	P-value
Age (yr)	56.31±16.55	53.94±13.37	0.169
Male sex	54 (55.1)	21 (60.0)	0.616
Body mass index (kg/m²)	25.03±3.15	25.07±3.69	0.555
ASA physical status			0.995
I	23 (23.5)	8 (22.9)
II	72 (73.5)	26 (74.3)
III	3 (3.1)	1 (2.9)
Tumor size (cm)	1.72±1.45	1.50±1.45	0.638
Benign tumor	2.47±1.69	1.99±1.57	0.917
Malignant tumor
Mean rank^a	31.87	25.54	0.246
Mean±SD^b	1.16±0.92	1.05±1.21	0.763
Tumor location (from the AV) (cm)	4.86±1.66	7.57±2.47	<0.001
Benign tumor	4.31±1.66	7.57±2.50	0.042
Malignant tumor	5.27±1.54	7.57±2.50	0.001
Benign tumor			0.985
Adenoma	29 (29.6)	9 (25.7)
Inflammatory/fibrotic/hyperplasitc polyp	10 (10.2)	4 (11.4)
Other (juvenile polyp/GIST/ schwannoma/lipoma)	3 (3.1)	1 (2.9)
Malignant tumor
Adenocarcinoma	13 (13.3)	4 (11.4)
pTis	5 (38.5)	4 (100)
pT1	6 (46.2)	0 (0)
pT2	2 (15.4)	0 (0)
Neuroendocrine tumor	43 (43.9)	17 (48.6)
Adenocarcinoma malignant tumor differentiation			0.164
Well	2 (15.4)	2 (50.0)
Moderate	10 (76.9)	1 (25.0)
Unknown	1 (7.7)	1 (25.0)
Neuroendocrine tumor malignant tumor differentiation			0.137
Low	37 (86.0)	17 (31.5)
Intermediate	6 (14.0)	0 (0)
Perineural invasion in malignant tumor^c			0.540
No	53 (98.1)	20 (100)
Yes	1 (1.9)	0 (0)

Values are presented as mean±SD or number (%), unless otherwise indicated. Percentages may not total 100 due to rounding.

CTA, conventional transanal approach; MTA, minimally invasive transanal approach; ASA, American Society of Anesthesiologists; SD, standard deviation; AV, anal verge; GIST, gastrointestinal stromal tumor.

^aMann-Whitney test.

^bStudent t-test.

^cThe subtotal differs from the total number due to missing data (CTA group, 54 patients; MTA group, 20 patients).

Table 2.

Comparison of pathologic and surgical outcome between two groups (n=133)

Outcome	CTA group (n=98)	MTA group (n=35)	P-value
Margin status (n=91)	70	21	0.131
Absent	63 (90.0)	21 (100)
Present	7 (10.0)	0 (0)
Lateral (n=91)	70	21	0.208
Absent	65 (92.9)	21 (100)
Present^a	5 (7.1)^a	0 (0)
Deep			0.295
Absent	95 (96.9)	35 (100)
Present^b	3 (3.1)^b	0 (0)
Safety margin (cm)
Lateral	3.51±2.67	4.00±3.35	0.424
Deep	2.83±3.30	3.69±4.34	0.102
Fragmentation			0.360
No	91 (92.9)	34 (97.1)
Fragmented	7 (7.1)	1 (2.9)
En bloc resection with margin negative			0.067
Yes	84 (85.7)	34 (97.1)
No	14 (14.3)	1 (2.9)
Blood loss (mL)	13.14±22.69	9.31±11.10	0.287
Operation time (min)	34.56±25.26	62.06±46.52	0.004

Values are presented as number only, number (%), or mean±standard deviation.

CTA, conventional transanal approach; MTA, minimally invasive transanal approach.

^aT2 adenocarcinoma (n=1), adenoma (n=3), and neuroendocrine tumor (n=1).

^bT2 adenocarcinoma (n=1), neuroendocrine tumor (n=1), and schwannoma (n=1).

Table 3.

Complication (n=133)

Complication	No. of patients (%)		P-value
Complication	CTA group (n=98)	MTA group (n=35)	P-value
None	91 (92.9)	30 (85.7)	0.117
Urinary difficulty	5 (5.1)	1 (2.9)
Bleeding	1 (1.0)	1 (2.9)
Other (postoperative fever, delirium)	1 (1.0)	3 (8.6)

Percentages may not total 100 due to rounding.

CTA, conventional transanal approach; MTA, minimally invasive transanal approach.

Table 4.

Recurrence in the CTA group

Variable	Case 1	Case 2
Pathology	Adenocarcinoma	Neuroendocrine tumor
Tumor size (cm)	2.2	0.5
Tumor location (from the AV) (cm)	6	4
T category or grade	pT1	Low grade
Margin status	Negative	Negative
Fragmentation	No	No
En bloc resection with negative margin	Yes	Yes
Recurrence-free survival (day)	672	220
Further treatment	Low anterior resection	CTA again

Case 1, rectal cancer, cT1 (SM1 invasion), margin 0.5 mm/deep margin 2 mm. Case 2, neuroendocrine tumor, G1, margin 1 mm/deep margin 0.5 mm.

CTA, conventional transanal approach.

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Minimally invasive transanal excision over conventional transanal excision: pursuing the perfect removal of early rectal cancer
HyungJoo Baik
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Minimally invasive transanal excision for rectal tumors: technical feasibility compared to conventional approach

Ann Coloproctol. 2025;41(2):162-168. Published online April 29, 2025

DOI: https://doi.org/10.3393/ac.2024.00864.0123

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Minimally invasive transanal excision over conventional transanal excision: pursuing the perfect removal of early rectal cancer

Minimally invasive transanal excision for rectal tumors: technical feasibility compared to conventional approach

Fig. 1. Intraoperative images of the transanal minimally invasive surgery (TAMIS) surgical procedure. (A) Marking around the tumor with bovie. (B) Appropriate traction using the hemoclip as a handle. (C) Complete full-thickness excision was performed.

Graphical abstract

Fig. 1.

Graphical abstract

Minimally invasive transanal excision for rectal tumors: technical feasibility compared to conventional approach

Characteristic	CTA group (n=98)	MTA group (n=35)	P-value
Age (yr)	56.31±16.55	53.94±13.37	0.169
Male sex	54 (55.1)	21 (60.0)	0.616
Body mass index (kg/m²)	25.03±3.15	25.07±3.69	0.555
ASA physical status			0.995
I	23 (23.5)	8 (22.9)
II	72 (73.5)	26 (74.3)
III	3 (3.1)	1 (2.9)
Tumor size (cm)	1.72±1.45	1.50±1.45	0.638
Benign tumor	2.47±1.69	1.99±1.57	0.917
Malignant tumor
Mean rank^a	31.87	25.54	0.246
Mean±SD^b	1.16±0.92	1.05±1.21	0.763
Tumor location (from the AV) (cm)	4.86±1.66	7.57±2.47	<0.001
Benign tumor	4.31±1.66	7.57±2.50	0.042
Malignant tumor	5.27±1.54	7.57±2.50	0.001
Benign tumor			0.985
Adenoma	29 (29.6)	9 (25.7)
Inflammatory/fibrotic/hyperplasitc polyp	10 (10.2)	4 (11.4)
Other (juvenile polyp/GIST/ schwannoma/lipoma)	3 (3.1)	1 (2.9)
Malignant tumor
Adenocarcinoma	13 (13.3)	4 (11.4)
pTis	5 (38.5)	4 (100)
pT1	6 (46.2)	0 (0)
pT2	2 (15.4)	0 (0)
Neuroendocrine tumor	43 (43.9)	17 (48.6)
Adenocarcinoma malignant tumor differentiation			0.164
Well	2 (15.4)	2 (50.0)
Moderate	10 (76.9)	1 (25.0)
Unknown	1 (7.7)	1 (25.0)
Neuroendocrine tumor malignant tumor differentiation			0.137
Low	37 (86.0)	17 (31.5)
Intermediate	6 (14.0)	0 (0)
Perineural invasion in malignant tumor^c			0.540
No	53 (98.1)	20 (100)
Yes	1 (1.9)	0 (0)

Outcome	CTA group (n=98)	MTA group (n=35)	P-value
Margin status (n=91)	70	21	0.131
Absent	63 (90.0)	21 (100)
Present	7 (10.0)	0 (0)
Lateral (n=91)	70	21	0.208
Absent	65 (92.9)	21 (100)
Present^a	5 (7.1)^a	0 (0)
Deep			0.295
Absent	95 (96.9)	35 (100)
Present^b	3 (3.1)^b	0 (0)
Safety margin (cm)
Lateral	3.51±2.67	4.00±3.35	0.424
Deep	2.83±3.30	3.69±4.34	0.102
Fragmentation			0.360
No	91 (92.9)	34 (97.1)
Fragmented	7 (7.1)	1 (2.9)
En bloc resection with margin negative			0.067
Yes	84 (85.7)	34 (97.1)
No	14 (14.3)	1 (2.9)
Blood loss (mL)	13.14±22.69	9.31±11.10	0.287
Operation time (min)	34.56±25.26	62.06±46.52	0.004

Complication	No. of patients (%)		P-value
Complication	CTA group (n=98)	MTA group (n=35)	P-value
None	91 (92.9)	30 (85.7)	0.117
Urinary difficulty	5 (5.1)	1 (2.9)
Bleeding	1 (1.0)	1 (2.9)
Other (postoperative fever, delirium)	1 (1.0)	3 (8.6)

Variable	Case 1	Case 2
Pathology	Adenocarcinoma	Neuroendocrine tumor
Tumor size (cm)	2.2	0.5
Tumor location (from the AV) (cm)	6	4
T category or grade	pT1	Low grade
Margin status	Negative	Negative
Fragmentation	No	No
En bloc resection with negative margin	Yes	Yes
Recurrence-free survival (day)	672	220
Further treatment	Low anterior resection	CTA again

Table 1. Demographic and clinical characteristics of patients undergoing transanal excision (n=133)

Values are presented as mean±SD or number (%), unless otherwise indicated. Percentages may not total 100 due to rounding.

Mann-Whitney test.

Student t-test.

The subtotal differs from the total number due to missing data (CTA group, 54 patients; MTA group, 20 patients).

Table 2. Comparison of pathologic and surgical outcome between two groups (n=133)

Values are presented as number only, number (%), or mean±standard deviation.

CTA, conventional transanal approach; MTA, minimally invasive transanal approach.

T2 adenocarcinoma (n=1), adenoma (n=3), and neuroendocrine tumor (n=1).

T2 adenocarcinoma (n=1), neuroendocrine tumor (n=1), and schwannoma (n=1).

Table 3. Complication (n=133)

Percentages may not total 100 due to rounding.

CTA, conventional transanal approach; MTA, minimally invasive transanal approach.

Table 4. Recurrence in the CTA group

Case 1, rectal cancer, cT1 (SM1 invasion), margin 0.5 mm/deep margin 2 mm. Case 2, neuroendocrine tumor, G1, margin 1 mm/deep margin 0.5 mm.