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Extended cold snare polypectomy for small colorectal polyps increases the R0 resection rate

Background and study aims  Despite widespread use of cold snare polypectomy (CSP), the R0 resection rate is not well documented. We perform extended CSP, resecting polyps with a > 1 mm circumferential margin. The aim of this study is to compare the R0 resection rate of extended CSP with conventional CSP and to assess safety. Patients and methods  From April 2014 to September 2016, 712 non-pedunculated colorectal polyps, < 10 mm in size, resected using CSP from 316 patients were retrospectively analyzed. Results  We divided lesions into conventional CSP (n = 263) and extended CSP groups (n = 449). The baseline characteristics of these two groups were not significantly different in univariate or multivariate analyses. Sessile polyps comprised 94 % (668/712), and the remaining were flat-elevated polyps. Mean size of polyps (±standard deviation) was 4.2 ± 1.5 mm. The most frequent pathology was low grade adenoma (97 %, 689/712). The R0 resection rate was significantly higher in the extended CSP group (439/449 [98 %]) than in the conventional CSP group (222/263 [84 %], P  < 0.001). There was no delayed bleeding or perforation in either group (conventional CSP group, 0/263, 95 % confidence interval: 0.0 – 1.4 % and extended CSP group, 0/449, 95 % confidence interval: 0.0 – 0.8 %). Conclusions  Extended CSP results in a higher R0 resection rate compared with conventional CSP. Extended CSP did not result in a higher rate of delayed bleeding or perforation. Extended CSP is a safe and promising procedure for endoscopic resection of non-pedunculated colorectal polyps < 10 mm in size

ABSTR AC T Background and study aims Despite widespread use of cold snare polypectomy (CSP), the R0 resection rate is not well documented. We perform extended CSP, resecting polyps with a > 1 mm circumferential margin. The aim of this study is to compare the R0 resection rate of extended CSP with conventional CSP and to assess safety.
Patients and methods From April 2014 to September 2016, 712 non-pedunculated colorectal polyps, < 10 mm in size, resected using CSP from 316 patients were retrospectively analyzed.
Conclusions Extended CSP results in a higher R0 resection rate compared with conventional CSP. Extended CSP did not result in a higher rate of delayed bleeding or perforation. Extended CSP is a safe and promising procedure for endoscopic resection of non-pedunculated colorectal polyps <10 mm in size Patients and methods

Study population
A retrospective review of 1304 consecutive polyps in 542 patients who underwent CSP for the treatment of colorectal polyps at the Utsunomiya Memorial Hospital (Utsunomiya, Japan) from April 2014 to September 2016 was performed. CSP was not performed for polyps with suspected carcinoma based on endoscopic findings. Data were collected from medical records, photographs and video recordings. Pedunculated polyps, ≥ 10 mm in size, undetermined resection method, hyperplastic and inflammatory polyp were excluded from this analysis. This retrospective study was approved by the Institutional Review Board prior to commencement.

CSP procedure
We divided the polyps into a conventional CSP group and an extended CSP group. The definition of extended CSP was a polyp resected with a more than 1 mm circumferential margin (▶ Fig. 1). We defined others as conventional CSP. An R0 resection was defined as an en bloc resection with pathologically negative resection margins [9]. Because of the low R0 resection rate using conventional CSP during the introductory period of CSP, we performed extended CSP since May 2015 to increase the R0 resection rate. Since that time, extended CSP was always attempted, however conventional CSP was occasionally performed because of technical problems due to location and peristalsis. Consequently, we mainly performed conventional CSP in the early phase of the study period, and performed extended CSP during the later period. The PCF-Q260AZI or CF-Q260AI (Olympus, Tokyo, Japan) was used. The polypectomy snare for CSP was an 11 mm, Extra Small Oval -Flexible, CAPTIVATOR TM II (Boston Scientific, Natick, MA, USA) or 10 mm, Oval, Snare-Master TM (Olympus, Tokyo, Japan). The resected polyp was suc- tioned and retrieved after CSP. Clip application was not performed. The retrieved polyp was preserved in formalin and assessed by routine histopathologic studies. The definition of delayed bleeding was overt bleeding within two weeks after the CSP.

Statistical analysis
Categorical data were compared by using the chi-squared test. Data with a normal distribution were compared with an independent t-test. To estimate the 95 % confidence intervals (CI) around the estimated proportions of patients with adverse events, we used the Clopper-Pearson exact method. Differences were considered to be statistically significant when P < 0.05. The above statistical analyses were performed using Bell-Curve for Excel 2015 software (Social Survey Research Information Co., Ltd. Tokyo, Japan). To evaluate potential confounding factors before resection, we used logistic regression analysis for multivariate analysis, performed using Statflex ver. 6.0 software (Artech Co. Ltd. Osaka, Japan).

Study population
Based on the exclusion criteria, 592 polyps in 226 patients were excluded as follows: pedunculated polyp (n = 327), ≥ 10 mm (n = 38), undetermined resection method (n = 51), hyperplastic (n = 168) and inflammatory polyp (n = 8). Consequently, data for 712 sessile colorectal polyps in 316 patients were included in this final analysis. The characteristics of these 316 patients are shown in ▶ Table 1. Seventy-eight of the patients were male and the mean age was 61. We divided them into conventional CSP (n = 119) and extended CSP groups (n = 197). Male gender was slightly more common in the conventional CSP group than in the extended CSP group (P = 0.113), and mean age was similar in both groups (P = 0.592).

Adverse events
The overall rate of adverse events was 0 % per procedure

Discussion
This study shows that extended CSP has a significantly higher rate of R0 resection compared to conventional CSP for nonpedunculated colorectal polyps < 10 mm. The safety of extended CSP is also demonstrated. CSP, which started in Western countries, is becoming more popular in Eastern countries as a simple and safe approach for resecting small colorectal polyps [5]. Since the malignant potential of small colorectal polyps is low, an almost zero rate of adverse events including delayed bleeding and perforation is important. CSP is suitable for the treatment of small colorectal polyps, because it has a shorter procedure time and lower rate of delayed bleeding than HSP or endoscopic mucosal resection [7,10]. The present study, which includes a large number of small non-pedunculated colorectal polyps, demonstrates that extended CSP is a promising method to increase the R0 resection rate. A low R0 resection rate (59 %) of small polyps resected by CSP has been reported [8]. We suggest two explanations for a low R0 resection rate. First, in preparing the specimen for pathological examination, determination of the exact margin for specimens resected by CSP is difficult because of a macroscopically unclear resection margin, since, unlike HSP, there is no cauterized area after CSP. Second, CSP makes a pathological diagnosis difficult microscopically because the resection margin of small colorectal polyps is not cauterized. Taken together, a resected polyp with adequate surrounding normal colonic mucosa is helpful to recognize the resection margin and to improve the quality of the pathological diagnosis.
Although intra-procedural bleeding is generally more common in CSP compared with HSP, the colonoscopist is rarely con-cerned with intra-procedural bleeding. Unlike delayed bleeding, persistent intra-procedural bleeding is easily controlled by applying a clip. CSP rarely leads to delayed ulceration after resection because of the lack of thermal injury. Anatomically, the submucosa has larger arteries and veins than the lamina propria. Delayed bleeding after HSP is usually caused by vascular damage in the submucosal layer due to use of the electrocautery. Generally, the rate of delayed bleeding after HSP is reportedly 1 -2 % [4,11], and the benefit of prophylactic clip application after HSP remains controversial [12,13]. When performing HSP, an extended mucosal resection without injection may involve the deep submucosa or muscularis, resulting in perforation. As reported by Horiuchi et al [6], CSP is less associated with injuries to the submucosa than HSP. Tuttici et al reported the characteristics of protrusions within the cold snare defect including submucosa and muscularis mucosa without an adenomatous component or vascular structure [14]. We believe that extended CSP may not damage the vessels in the submucosal layer. Therefore, extended CSP does not increase the rate of delayed bleeding and perforation. The 95 % CI for the rate of delayed bleeding in the extended CSP group in the present study was less than 1 %.
For the treatment of colorectal tumors, an en bloc R0 resection is important to determine the completeness of resection and to decrease the rate of local recurrence [5]. En bloc resection is defined as a tumor removed in one piece, and R0 resection is defined as an en bloc resection with negative pathologic margins. Although endoscopic resection of small colorectal polyps is usually straightforward, local recurrence after polypectomy necessitates additional resection performed by CSP, HSP, endoscopic mucosal resection or endoscopic submucosal dissection. Unlike the first endoscopic treatment, when treating a recurrent lesion one frequently encounters severe submucosal fibrosis due to the first resection, making the resection difficult. To decrease the need for additional resection, the extended CSP is a viable option. Further, we recognize that CSP involving surrounding normal mucosa has become a standard strategy [15]. The technique referred to here as an "extended CSP" may represent the standard technique advocated by experts used in the clinical practice of CSP. However, to date, there is no significant evidence reporting the superiority of this extended CSP strategy over conventional CSP. Although the pathological significance of extended CSP compared with conventional CSP should ideally be shown by a randomizedcontrolled trial, the superiority of extended CSP is obvious and such a clinical trial may be difficult to conduct.
We recognize some acknowledged limitations of this study. First, the study is limited by its retrospective design and several potential biases. Both techniques were compared indirectly in two different periods and the impact of the learning curve of the endoscopists and pathologists cannot be excluded. The pathologists who assessed completeness of resection could not be blinded to the procedure performed. However, an extended CSP is reasonable to improve the R0 resection rate, and no adverse events occurred in this study including a large number of CSP procedures. Second, there is no evaluation of local recurrence after CSP in this study. CSP as a long-term outcome remains unclear [7,15]. Third, this study did not include pedunculated polyps but only non-pedunculated polyps < 10 mm in size. Therefore, this result should not be extrapolated to CSP for pedunculated colorectal polyps. Generally, pedunculated polyp have a large vessel with greater potential for delayed bleeding [16].

Conclusion
In conclusion, this study shows that extended CSP results in a higher R0 resection rate for non-pedunculated colorectal polyps < 10 mm compared with conventional CSP. Extended CSP did not result in a higher rate of delayed bleeding or perforation. To our knowledge, this is the first report of the safety and efficacy of extended CSP in compared with conventional CSP. Extended CSP is a safe and promising procedure for endoscopic resection of non-pedunculated colorectal polyps < 10 mm in size.