Endoscopic mucosal resection (EMR) is widely used in Western centers for the treatment of non-pedunculated colorectal adenomas >2 cm in size. Colonic endoscopic submucosal dissection (ESD) for the treatment of these adenomas is rarely performed outside of Japan and Korea [1]. EMR is associated with a low risk of adverse events, rapid procedure times, and relatively low technical complexity; it is also suitable for outpatient treatment as patients generally only need to be observed for a few hours after the procedure and can go home the same day [2]. ESD is technically complex, involves a long procedure time, and is associated with a significant risk of intraprocedure and delayed colon perforation; patients require hospitalization for observation after the procedure [3]. The main advantage of ESD is the excellent rate of en bloc resection, which reduces local recurrence rates and ensures precise histopathologic staging if malignancy is detected. However, advances in endoscopic optics have improved the visual assessment of malignancy, and improvements in endoscopic techniques have significantly reduced the local recurrence rate after EMR and facilitated the treatment of recurrences. EMR is therefore likely to continue as the widely used technique for the treatment of large colorectal adenomas in the West.

The majority of recurrences after EMR are unifocal and <5 mm in size [4]. Over 90% of the recurrences can be treated with conventional snare polypectomy, EMR, or ablation [4]. A second recurrence is found in 10% to 40% of all patients after treatment of the first recurrence [4,11]. Underwater EMR appears to be superior to conventional EMR for treating recurrences, with a higher rate of complete removal of visible neoplasia and a lower second recurrence rate [11]. Even lesions that recur two or more times can be treated successfully with additional EMR or underwater EMR [13]. Treatment of recurrences with EMR or underwater EMR appears to be as safe as the treatment of naive lesions, with a low risk of bleeding or perforation [4,11,13]. Progression to malignancy during treatment is very rare [4,13].

In expert centers, ESD enables complete en bloc resection of >85% of all colorectal adenomas and superficial cancers [3]. In contrast, en bloc resection rates for colorectal adenomas >2 cm in size are typically 25% or less with EMR [8]. Adenoma recurrence is significantly more common with EMR than with ESD: recurrence rates for adenomas >2 cm in size treated with EMR are typically approximately 16% in Western centers [4] and 7% in Japanese centers [13], while recurrence rates with ESD are 1.4% in Japan [13]. However, ESD requires significantly longer time to perform than EMR: the mean procedure time for EMR in a large Western study was 25 minutes while that for ESD in a large Japanese study was 116 minutes [2,3]. In the same two studies, perforation occurred in 1.3% of the patients undergoing EMR and in 4.9% of the patients undergoing ESD. Hospitalization was required in <10% of the Western patients who underwent EMR, while 100% of Japanese patients undergoing colorectal ESD are typically hospitalized for >3 days [14].

While piecemeal EMR of adenomas results in good clinical outcomes in most patients, en bloc resection with ESD is preferable for cancers with slight submucosal invasion and favorable histologic features, as it provides curative endoscopic treatment without the need for surgery [15]. Piecemeal resection with EMR may reduce the accuracy of histologic analysis and may lead to poor oncologic outcomes due to local recurrence. With current technology, endoscopic differentiation between adenoma and cancer is only 70% to 90% accurate, and the accuracy of differentiating between slight and deep submucosal invasion is only 70% to 80%; therefore, precise histologic staging with an en bloc resection using ESD is preferable for lesions that have a significant likelihood of being invasive cancers [15].

EMR is safe and effective for treating colorectal adenomas. Compared with ESD, EMR is significantly faster to perform, has a much lower perforation rate, and does not require post-procedure hospitalization. Advances in EMR techniques have led to reduced local recurrence rates, and the modern treatment of recurrences is technically simple, safe, and usually effective. While ESD in expert centers still offers a superior technical result and lower recurrence rate, the procedural complexity, additional unreimbursed procedure time, perforation risk, and requirement of post-procedure hospitalization make it unlikely to be widely adopted in the West for treatment of colorectal adenomas. Improvements in endoscopic visual assessment of early submucosal invasive cancer may enable identification of a limited number of patients who may be suitable candidates for ESD in Western centers, if additional data showing safety and long-term efficacy comparable to surgery become available.