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transanally together with standard laparoscopic camera and a standard CO insufflator. This approach
2
has now been well accepted as it does not incur additional costs and has a lower learning curve. Besides
aiding in excision of rectal lesions, this method has been adopted for a variety of other procedures such
as transanal total mesorectal excision (TME), repair of rectovaginal/rectourethral fistulas, repair of
anastomotic complication after low anterior resection, etc. This review details the progress of transanal
surgery and the use of TAMIS in different scenarios.

TAMIS FOR LOCAL EXCISION OF RECTAL LESIONS
Since Park technique was first described in 1968, approaches for local excision of rectal tumors have
[4]
undergone many changes. TAE evolved to TEM, which was first described by Buess et al. . However,
this approach was not popularized due to the cost and the steep learning curve. With the advancement
[5]
in natural orifice transluminal endoscopic surgery, TAMIS was introduced in 2009 . Now, TAMIS is a
reasonably good platform for the local excision of multiple rectal neoplasms, such as benign adenomas,
lesions with high grade dysplasia, neuroendocrine tumors, and well-selected malignant rectal lesions.

INDICATION
The indications for TAMIS do not differ from those of TAE or TEM for both benign and malignant
lesions that have been assessed preoperatively with endoscopy and complimented by endoanal/endorectal
[6-8]
ultrasonography and/or magnetic resonance imaging . For benign lesions, it could be large adenoma,
high grade dysplasia, or incompletely excised lesion through colonoscopy. For malignant lesions, early
rectal cancers that are confined to the submucosal layer (T1 lesions) are best suited for TAMIS.

T1 adenocarcinoma of the rectum can be categorized into low-risk lesions and high-risk lesions based on
the risk of recurrence/metastasis. This can be further categorized into low-risk T1 adenocarcinomas of
the rectum, which are described as small lesions less then 4 cm in diameter; Haggits 1-3 lesions; Kikuchi
[6]
sm1 lesions; and well-differentiated cancer with no lymphatic, vascular, or perineural invasion . High-risk
lesions are Haggits 4; Kikuchi sm2/sm3, poorly differentiated tumors; signet cell lesions; presence of tumor
budding; lymphovascular involvement; absence of lymphoid infiltration; and young patients (< 45 years old).
This is due to T1 lesions having risk of LN metastasis of up to 10%-15%. However, with sub analysis, sm1
lesions only carry 1%-3% risk of lymph node (LN) metastasis while the risk increases to 8% for sm2 lesions
and 23% for sm3 lesions. Similarly, Haggits 1-3 lesions have less than 1% risk of lymph node metastasis,
while, for Haggits 4 lesions, the risk is about 12%-15%. Hence, high-risk lesions should ideally be treated as
[7,8]
T2 lesions and they should be discussed in multi-disciplinary team meetings for a holistic approach of
management.

It is sometimes difficult to distinguish T1 or T2 lesions preoperatively, and, for these, TAMIS could be a
platform for the resection of these lesions and guide the further management based on the final pathology
report. Hence, it is wise to counsel these patients on the possibility of formal radical resection if the
pathology report is unfavorable, high-risk T1 or T2 lesions. TAMIS resection could also be an option for
palliation for T3 tumors when patients are unfit to undergo a radical resection.

SAFETY AND FEASIBILITY
Multiple studies have been published on the safety and feasibility of TAMIS [5,9-17] , with Albert and Atallah
publishing one of the biggest series. They reported an overall loco-regional recurrence rate of 4.3%, with
[16]
positive margins of 6% in their 20-month follow up study , whereas Keller and Haas reported 6.6% of their
[13]
patients with positive margin and only one patient had local recurrence at median follow up of 39.5 months .

Penetration into the peritoneal cavity is unavoidable during local excision of malignant lesions that are
[18]
located at the anterior wall of the upper rectum (above the peritoneal resection). Chen et al. reported