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Endoscopic submucosal dissection (ESD) affords a high rate of en bloc resection and represents advancement in the endoluminal treatment of early gastrointestinal (GI) neoplasms. Despite its well-established role in curative resection of early gastric and esophageal squamous cancers, its application to colorectal neoplasms remains controversial. In a recent issue of the Journal of Gastroenterology and Hepatology, Uraoka et al. address the current issues regarding colorectal ESD with special emphasis on training and implementation of ESD.[1] Before it can become standardized, several issues still need to be carefully considered.

Compared with conventional endoscopic mucosal resection (EMR), colorectal ESD is technically difficult, time-consuming, carries a higher risk of perforation, and has a long learning curve. To master this procedure, endoscopists should ideally start with gastric and esophageal ESD so that they can familiarize themselves with the technical aspects of this procedure. The paucity of gastric cancer with the resultant lack of cases for ESD, however, is a common hurdle that most Western countries have encountered at the early stages of developing a colorectal ESD program. According to a Japanese study that focused on the learning curve required to master colorectal ESD, one becomes safe in avoiding perforation after approximately 40 procedures and becomes proficient after approximately 80 procedures.[2] Therefore, the establishment of a feasible and effective training model, either using animal models or hands-on training under the guidance of an expert endoscopist, is the first step in implementation of colorectal ESD.

Colorectal neoplasms are biologically different from gastric or esophageal neoplasms in terms of invasiveness and the natural course of the disease. Cancers of the upper GI tract do not arise via the adenoma-carcinoma sequence; most cases are considered as developing de novo. They also carry a higher malignant potential so that the risk of metastasis is higher at a relatively shallow depth of invasion; thus, en bloc resection at the time of diagnosis becomes crucial. En bloc resection is also mandatory in order to minimize the risk of recurrence or residual cancerous lesion. On the other hand, the pathologist can have a complete endoscopic specimen with minimal cauterization artifact and, thus, be able to make a thorough evaluation. Conversely, colorectal neoplasms, especially noncancerous ones, progress along a relatively indolent course. For this reason, re-EMR or ablation with argon plasma coagulation is still feasible, should any residual neoplasm be identified at surveillance colonoscopy. Moreover, even within the spectrum of colorectal neoplasms, lesions with different morphology carry different risks of deep invasion. For example, depressed type neoplasms can have as high as 50% malignant transformation at the time of diagnosis and submucosal invasion at a size of 1.5–2 cm.[3-5] 0-IIa (laterally spreading tumor, nongranular type), especially the pseudodepressed type lesions, may have not only a higher rate of deep invasion but also present in a pattern of multifocal invasion when compared with its counterparts.[6, 7] Accordingly, en bloc resection is indispensable for such lesions and provides a more accurate pathological assessment that reduces the risk of recurrence and undertreatment. In this context, defining the true candidate lesions for colonic ESD is necessary to avoid overtreatment and the resultant significant complications. Accordingly, in my view, colorectal ESD should be confined to a limited category of lesions based on a detailed endoscopic assessment of the risk of deep invasion.

Another consideration in overall management is that compared with gastrectomy or esophagectomy, colectomy is less invasive with less postoperative morbidity, especially when it is performed for proximal colonic lesions. Further, laparoscopic surgery is far less invasive than conventional laparotomy and has its advantages over ESD in terms of whole layer resection and lymph node dissection. Moreover, when the endoscopist encounters severe complications, such as perforation that cannot be closed with colonoscopic clipping, most cases need laparotomy. Thus, the duration of hospitalization will be much longer, which could have been avoided if the lesion were initially resected with laparoscopy.

Although reported perforation rates from Japanese centers range from 4.9% to 12% and most of these could be managed primarily with endoscopy, there could be publication bias; the real-world data are largely unreported. Moreover, institutions with high case volumes of colorectal ESD had significantly lower rates of severe complications.[8] Most early colorectal neoplasms can be managed adequately with either polypectomy or EMR/piecemeal EMR (EPMR). For this reason and also given the low prevalence of cases for which colorectal ESD is indicated, it is reasonable to advocate management of such lesions in high-volume units, thereby ensuring better quality of care and optimal outcomes.[9, 10]

Currently, there is a lack of randomized clinical trials comparing ESD and laparoscopic surgery regarding short-term outcome and long-term effectiveness for management of early colorectal neoplasms. Thus, further study is needed. Moreover, anatomical subsite-specific analysis (e.g. rectum vs colon) would be necessary because the benefit of colorectal ESD may vary by anatomical sites with regards to complication risk, quality of life, cancerous recurrence, or survival.[11, 12]

The accuracy of endoscopic diagnosis of colorectal neoplasms and the pathological assessment of each endoscopic specimen remain important issues. The ability to make the correct diagnosis of lesion morphology and invasion depth plays a pivotal role in proper management. Thus, knowledge regarding the colorectal neoplasm is of utmost importance for selecting candidate lesions for ESD. In this respect, application of high-magnification colonoscopy and image-enhanced endoscopy (IEE) is mandatory. However, high-magnification colonoscopy and IEE are still not popular in many countries outside Japan, especially the chromoendoscopy technique using indigo-carmine dye spraying or crystal violet staining. The former can enable correct morphological diagnosis, and the later enables precise observation of the surface pit pattern (especially Kudo type V pit pattern), thus making highly accurate prediction of invasion depth possible.[13-15] Similarly, inaccurate diagnosis leads to inappropriate use of ESD and may cause resultant undertreatment of submucosal invasive cancerous lesions or overtreatment of neoplasms that could have been properly and easily treated with EMR or EPMR. Pathological assessment is another critical issue. While Japanese pathologists assess each endoscopic specimen in detail using 1- to 2-mm slice intervals, it is unclear whether pathologists in other countries are able or willing to do this, given limited time and reimbursement. Without detailed pathological evaluation of each ESD specimen, this procedure will lose its value as a reliable curative procedure, possibly leading to an increased risk of postcolonoscopy colorectal cancer.

Finally, the cost-effectiveness of this procedure remains unclear. The high costs of colorectal ESD, especially regarding time and manpower, are a barrier to its popularization. It requires a longer procedure time, more manpower, and expensive endoscopic equipment/devices. Its high complication rate and unclear long-term outcome add to the ambiguity regarding standardization of this procedure.

In summary, the demand for en bloc resection and true indications for colorectal ESD do exist, but several barriers exist before its general clinical application and standardization can be achieved. To solve this dilemma, further large-scale studies from different countries are urgently required that take into account both time and expense.

References

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