We searched databases including PubMed, EMBASE, the Cochrane Library, and Science Citation Index updated to August 2013 to identify related articles in English language that compared EMR and ESD. All bibliographies were indentified in the reference lists. The searching terms used were “EMR or endoscopic mucosal resection” and “ESD or endoscopic submucosal dissection”. Major proceedings of international conferences (such as Digestive Disease Week, Asian Pacific Digestive Week, and so on) were also hand-searched.

The inclusion and exclusion criteria are shown in Table 1.

Data were extracted by one investigator and confirmed by the other according to a predefined data extraction form. Disagreements were resolved by consultation with a third investigator. The following data were collected: year of publication, first author, country, duration, number of participants and lesions in each group, age, tumor size and endpoints (en bloc resection rate, histological resection rate, local recurrence rate, operation time and complications). The definitions of the endpoints were: (1) en bloc resection rate - en bloc removal of tumors in one piece without fragmentation; (2) histological resection rate - complete resection of tumors with no local tumor residue in both margin and basal sites; (3) local recurrence rate - a histological diagnosis of tumor at the resected site during follow-up; (4) operation time - from marking to resection of the lesions; and (5) rate of complications - procedure related bleeding or perforation incidence during or after the operation. The Newcastle-Ottawa Scale was used to assess the quality of the included non-randomized studies.

All data extracted were entered in the freeware program Review Manager (Version 5.0 for Windows, Cochrane Collaboration). The weighted mean difference was calculted for continuous data, and the odds ratio (OR) with 95%CI was used for dichotomous data. Statistical heterogeneity between trials was evaluated by the χ² test and was considered to be present at P < 0.1. We also used I² to assess the heterogeneity. I² > 50% was considered statistically significant. In the presence of statistical heterogeneity, heterogeneity was explored by subgroup analysis or a random-effects model. Publication bias was detected by a funnel plot, and then the symmetry of the funnel plot was confirmed by the Egger’s test, with a P value of 0.05.

A total of 706 potential studies were retrieved for the meta-analysis, and 538 were excluded for not including the colorectal or rectal tumors, and 162 were excluded because EMR and ESD were not compared. The remaining six eligible studies[9-14] were chosen for further analysis (Figure 1). A total of 1642 lesions were included in the meta-analysis, including 776 lesions in the ESD group and 866 lesions in the EMR group. All of the studies were respective case-control studies, not randomized controlled trials (RCTs). The key characteristics of the studies are listed in Table 2.

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Figure 1 Flow diagram of trial selection.

The en bloc resection rate was reported in five studies[9,11-14]. Because heterogeneity was detected (P = 0.0004; I² = 80%), a random effect model was applied. The analysis showed a higher en bloc resection rate in the ESD group (604/687) than in the EMR group (306/688) (OR = 7.94; 95%CI: 3.96-15.91) (Figure 2A). Based on the result of the sensitivity analysis, we excluded the study with smallest samples[12], but the heterogeneity could not be eliminated (P = 0.0006; I² = 83% ).

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Figure 2 Comparing endoscopic submucosal dissection and endoscopic mucosal resection. A: En bloc resection rate; B: Histological resection rate; C: Local recurrence rate; D: Procedural time; E: Procedure-related complications. ESD: Endoscopic submucosal dissection; EMR: Endoscopic mucosal resection.

The histological resection rate was reported in three studies[10,13,14]. A random effect model was applied because of the heterogeneity (P < 0.00001, I² = 94%). The analysis showed no significant difference in histological resection rate between the ESD group (434/518) and the EMR group (310/473) (OR = 1.65; 95%CI: 0.29-9.30) (Figure 2B). We ruled out the study from Japan[10], and heterogeneity still existed (P < 0.00001, I² = 95%).

All of the studies reported the local recurrence after operation. There was no heterogeneity in the studies (P = 0.31, I² = 16%), and a fixed effect model was applied. The local recurrence rate was higher in the EMR group (106/832) than in the ESD group (7/712) (OR = 0.09; 95%CI: 0.04-0.19) (Figure 2C).

The operation time for ESD vs EMR was reported in four studies. Only two[9,11] were included in the meta-analysis for the reason that one study provided only median operation time and the operation time of ESD group was divided into two parts in the other study. A random effect model was applied because of the heterogeneity (P = 0.0007, I² = 91%). Longer time was needed in the ESD group than in the EMR group (Figure 2D).

Data for procedure-related complications were reported in all of the studies included. There was heterogeneity among the studies (P = 0.04, I² = 58%). We excluded two studies from Korea[13,14], and eliminated the heterogeneity (P = 0.15, I² = 43%). A fixed effect model was applied, the subsequent analysis showed that there was no statistical difference between the two groups (OR = 1.59; 95%CI: 0.92-2.73) (Figure 2E).

We used the en bloc resection rate as the outcome, and no publication bias was detected by funnel plot and the Egger’s test (P = 0.217).

Endoscopic submucosal dissection (ESD) was originally developed for en bloc resection of lager, flat gastrointestinal tumors. Compared with endoscopic mucosal resection (EMR), ESD was considered to be more time consuming and have more complications for the treatment of colorectal tumors.

There is no current consensus on the optimal endoscopic method for the treatment of colorectal tumors. Authors conducted a systematic review to compare the efficacy and safety of EMR and ESD for the treatment of colorectal tumors.

Authors designed the meta-analysis to systematically evaluate the two techniques, ESD showed considerable advantages over EMR for colorectal tumors regarding en bloc resection rate and local recurrence rate, without increasing the procedure-related complication rate. They provide evidence for endoscopic treatment of colorectal tumors.

The conclusions of this meta-analysis can help the endoscopists to select the right tool to treat colorectal tumors.

EMR is an endoscopic technique developed for removal of sessile or flat neoplasms confined to the superficial layers (mucosa and submucosa) of the gastrointestinal (GI) tract. A principle EMR consists of three steps: marking, lifting, and cutting. ESD is a newly developed technique in which submucosal dissection is carried out using an electrocautery knife to acquire a single-piece specimen, it is developed for en bloc removal of large (usually more than 2 cm), flat GI tract lesions.

This article of a meta-analysis of ESD vs EMR for the treatment of colorectal tumors with interest. ESD for colorectal lesions is still a developing area with a short history compared to ESD for gastric tumors. Since there is no prospective study assessing the efficacy of colorectal ESD, a meta-analysis of retrospective data of EMR and ESD is thus helpful in comparing the two procedures.