INTRODUCTION
Endoscopic mucosal resection (EMR) is widely accepted and regularly used for treatment of precancerous and early colorectal neoplasms. However, this technique is not feasible and safe for
en bloc resection if the tumor size is larger than 20 mm, as it may not facilitate accurate histologic diagnosis and reduced recurrence rates [
1-
4].
Endoscopic submucosal dissection (ESD) is a recently developed therapeutic alternative to EMR. ESD has the advantages of allowing
en bloc resection, irrespective of tumor size, location, and shape for precise histologic evaluation and reduction of local recurrence. However, ESD requires advanced technique and its procedure time is longer than EMR. Also, it has a considerable risk of complications such as bleeding and perforation, and has a long learning curve [
1-
5].
Colorectal laterally spreading tumors (LSTs) are superficial and flat neoplasm that are larger than 10 mm in diameter; LSTs have a short axis that extends laterally along the colorectal luminal wall. LSTs are divided into 2 types: the granular and the nongranular type. The granular (LST-G) type is divided into 2 subtypes: homogeneous (HG) subtype and nodular mixed (NM) subtype. The nongranular (LST-NG) type is divided into 2 types: flat elevated (FE) subtype and pseudo-depressed (PD) subtype according to their endoscopic macroscopic morphology during chromoendoscopy with indigo carmine dye spraying [
6-
9].
Submucosal invasive cancer is less frequent in LSTs than in polypoid lesions of similar size [
6-
9]. Therefore, EMR or ESD is used to treat LSTs [
3,
10-
18]. However, the clinicopathological characteristics of LSTs and risk of cancer are different among types and subtypes according to their endoscopic macroscopic morphology [
19-
24]. Submucosal invasive cancers are more frequent in the nongranular type than in the granular type. PD, NM, and larger LSTs have a higher malignant potential [
19-
24]. Thus, to avoid either unnecessary surgery or incomplete resection in treatment of LSTs, it is crucial to keep in mind the differences in malignant potential to select the appropriate therapeutic modality for specific LST types and subtypes.
ESD has been considered the optimal therapeutic modality for larger colorectal lesions, and the clinical outcomes of ESD in treatment of larger lesions have been reported [
1-
5]. However, there is lack of data about clinicopathological features of patients with LSTs treated by ESD. In this study, we investigated the clinicopathological features of patients with LSTs treated by ESD, and assessed the treatment outcomes of ESD.
DISCUSSION
Superficial colorectal neoplasms, including precancerous adenoma and early colorectal cancer, are now increasingly detected by screening colonoscopy and recent advances in techniques such as chromoscopic and magnification colonoscopy [
7-
9]. According to recent studies, 7% to 36% of diagnosed colorectal neoplasms are flat or depressed lesions; these are usually removed by endoscopic resection, which is minimally invasive [
7-
9]. Colorectal LSTs are large and superficial flat neoplasms, and most are adenomatous lesions [
6-
9]. Therefore, colorectal LSTs are considered good candidates for endoscopic resection [
10].
EMR is useful for precancerous lesions and early superficial colorectal cancer. However, it is very hard to perform
en bloc resection of a colorectal neoplasm that is larger than 20 mm due to snare size limitation. Large colorectal neoplasms can be removed by piecemeal EMR. However, this makes it difficult to obtain a precise histopathological diagnosis. Also incomplete resection and local recurrence rates are high in piecemeal EMR [
1-
4]. Therefore, EMR and piecemeal EMR are unsuitable for the treatment of colorectal neoplasms that is larger than 20 mm in diameter, including LSTs.
ESD is a practicable endoscopic procedure for large colorectal neoplasms because it provides
en bloc specimens for accurate histopathologic diagnosis, regardless of lesion size or location, enabling precise determinations of tumor margin and invasion. However, colorectal ESD is technically difficult and has a significant risk of complications such as perforation because the colon has thin wall, sparse muscle layer, tortuous and multiple folds, and peristalsis [
1-
5]. Therefore, colorectal ESD is no longer widely used as a standard method for treating colorectal neoplasms, but has been applied in clinical research settings at advanced institutes. Nevertheless, previous reports showed that ESD of colorectal neoplasms was associated with a higher rate of
en bloc resection (61.0%-98.2%) and curative resection (58.0%-95.6%), and a lower risk of recurrence (0%-11%) [
5].
At first, we evaluated the efficacy and safety of ESD removal of colorectal LSTs. In our study, rate of
en bloc resection was 89.0% and rate of R0 resection was 85.7%, with a mean size of 33.3 mm. Our results are comparable to those in previous studies [
5], and indicate that ESD provides a high rate of
en bloc and complete resection for colorectal LSTs.
Because of recent innovations in technique and equipment, ESD has become easier and safer over time. However, compared to EMR, ESD is still associated with significant complications such as bleeding (0.5%-9.5%) and perforation (1.4%-8.2%) [
5]. According to our study, the bleeding rate and perforation rate after ESD were 5.2% and 1.9%, respectively, similar to those in previous reports [
5]. These results suggest that ESD may be acceptable for treating large colorectal neoplasms such as LSTs because of its high rate of
en bloc resection and curative resection, even though it is associated with significant complications such as bleeding or perforation.
Next, we compared the outcomes of ESD according to endoscopic macroscopic types and subtypes. In mean procedure time, en bloc resection rate, R0 resection rate, bleeding rate, or perforation rate, there were no significant differences between LST-G and LST-NG types; however, if only small perforations are considered, the frequency was higher in LST-NG than in LST-G types.
Chromo- and magnifying endoscopy with indigo carmine dye are useful for characterizing lesions based on the morphologic architecture of colonic mucosal crypt orifices (pit pattern classification) [
9]. Specifically, the cancerous type V pit pattern is sub-classified into type V
I and type V
N. Type V
I indicates adenoma with severe dysplasia or SM1 carcinoma and type V
N indicates invasion more than SM1. The Kudo pit pattern classification is a very precise diagnostic method that is used to predict the depth of invasion of colorectal neoplasms [
9].
Previous studies reported that the frequency of submucosal invasion by colorectal LSTs increased with size; LST-NG type had much higher rate of submucosal invasion than that of the LST-G type. Moreover, the rate of submucosal invasion by the NM subtype and PD subtype was significantly higher than that of the HG subtype and FE subtype [
19-
24]. In our study, no significant differences were found in frequency of cancerous pit pattern (Vi/Vn) and adenocarcinoma between LST-G and LST-NG types. However, the rate of cancerous pit pattern was significantly higher in PD subtype than in FE subtype, and tended to be higher in NM subtype than in HG subtype; moreover, the incidence of adenocarcinoma in the PD subtype and NM subtype was significantly higher than in the HG subtype and FE subtype, similar to that in previous reports [
19-
24]. These data suggest that different strategies may be required for treating LSTs according to their macroscopic types and subtypes. Therefore, it is critical to predict the depth of invasion by using chromo- and magnifying endoscopy, and to assess malignancy based on LST types and subtypes before selection of a therapeutic modality. If ESD is considered, these lesions must be cautiously removed
en bloc to ensure accurate histopathological diagnosis.
A major limitation of our study is that we could not perform multivariate analyses including well-known factors related with outcomes of colorectal ESD such as fibrosis, procedure time, en bloc resection versus piecemeal resection, complete vs incomplete resection, and so on.
However, according to our study we can conclude that the appropriate treatment of colorectal LSTs should be determined based on their macroscopic types and subtypes, and on pit pattern findings. ESD is acceptable and promising for colorectal LSTs with regard to en bloc resection, curative resection, and risk of complications.