Cold snaring diminutive polyps: can we make of a polyp … a better polyp?

 

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Colorectal cancer (CRC) is a major cause of morbidity and mortality in Western countries [1] [2]. A high quality randomized trial recently showed the efficacy of endoscopic polypectomy in preventing CRC incidence and mortality [3], confirming the results of previous observational studies [4] [5]. Completeness of endoscopic resection is necessary to prevent post-polypectomy recurrence and interval cancer [6]. However, endoscopic polypectomy also carries a definite risk of major adverse events, such as bleeding or bowel perforation [7], so that a careful balance between efficacy and safety appears to be clinically relevant.

Most polypectomies are performed for diminutive (< 5 mm) or small (6 – 9 mm) lesions, which represent over 90 % of all polyps [8]. To minimize the risk of adverse events, techniques of cold polypectomy, that is, without electric current, by means of biopsy forceps or snare have been proposed [9]. Despite widespread adoption in clinical practice, only a few studies have aimed to standardize the technique of cold polypectomy [10] [11] [12], so that a high degree of technical heterogeneity among endoscopists persists [13].

Most of the available studies have looked at what might be the optimal device for cold polypectomy. Conventional forceps appeared to be suboptimal with incomplete resection rates of 24 % – 61 % [14] [15] [16]. Jumbo forceps provided better endoscopic but not better histological rates of complete resection [15]. Cold snaring possesses the advantage of guillotining the tissue in a single piece, including 1 – 2-mm margins of normal surrounding tissue [17]. Cold snaring has been shown to be superior to removal by biopsy forceps in terms of both histologic eradication rate and procedure-related time [16]. Cold snaring has been also shown to be superior to hot snare polypectomy [10] [11] [12]. In addition, the use of mini-snares specifically designed for cold snaring (cold polypectomy snare, Exacto; US Endoscopy, Mentor, Ohio, USA) has been shown to further increase the rate of complete resection [18].

It could be argued, however, that the main reason for the unfeasibility of cold snaring is not so much related to the device itself, but to polyp morphology. When a tiny lesion is only slightly or not at all elevated, cold snaring may be either unfeasible or incomplete, so that conventional forceps are still used despite this being suboptimal [13]. Thus, a Copernican revolution in the field of cold snaring may be needed, namely, not to further change the device, but to change the polyp itself. In other words:

Can we make of a polyp … a better polyp?

In this issue of Endoscopy, Din and colleagues report on their systematic application of the “suction pseudopolyp” technique to subcentimetric polyps, in an attempt to make the shape of these lesions more suitable for cold snaring [19]. The suction pseudopolyp technique was first described in an Australian study [20]. It consists of aspirating the tiny lesion into the suction channel of the colonoscope for a few seconds, reshaping it in a protuberant pseudopolyp that can be easily ensnared. In the original study, Pattullo and colleagues limited application of the technique to subcentimetric flat nonpolypoid lesions, and showed complete endoscopic resection in 100 % of the polyps, without immediate or delayed adverse events [20]. Such a suction-based technique appears more appealing compared with the classic injection technique, since it is less time- and resource-consuming [20]. In this issue of Endoscopy, Din et al. describe taking the suction pseudopolyp technique a step further, namely they apply it to all subcentimetric lesions, regardless of their shape [19]. In a well-designed monocentric trial, 148 polyps of size 3 – 7 mm were randomized between the standard cold snaring and the new suction-based technique. Although completeness of excision tended to be higher with the new compared with the standard technique, both endoscopically (98.6 % vs. 92.6 %, P = 0.08) and histologically (76.3 % vs. 63.8 %, P = 0.14), the differences were not statistically significant [19].

The main strength of this study has been to show the high feasibility and the very high level of efficacy of the suction pseudopolyp technique, regardless of the polyp morphology [18]. Differently from the Australia study, most of the lesions included were categorized as Paris classification Is, with fewer than 15 % being IIa/b [19] [21]. The 98.6 % endoscopic complete resection rate achieved by Din et al. in mostly sessile polyps is very similar to the 100 % reported by Pattullo et al. for nonpolypoid lesions, thus expanding the suction-based technique to Is polyps. In addition, Din et al. tested the suction-based technique purely in association with cold snaring, while both hot and cold snaring were allowed in the Australian study [19] [20]. Thus, the current study clearly shows that the suction-based technique may be coupled with cold snaring, at least for polyps < 7 mm, regardless of the location and the histology of the polyp. Nevertheless, it could be argued that the new suction-based technique failed to achieve statistically significant superiority compared with the standard technique, presenting a question about its usefulness in clinical practice. However, this appeared to be related not to a suboptimal performance of the new technique, but to a better than expected performance of the standard cold snaring: the latter showed a 92.6 % rate of endoscopic complete excision, whilst a conservative assumption of 86 % had been used for the sample size calculation [19]. This unexpectedly high efficacy in the standard cold snaring arm might at least in part be attributed to the selected snare. As already outlined above the Exacto mini-snare, that was used in both study arms, has been specifically designed with a thinner wire to improve the rate of complete excision with cold-snaring; such improvement has already been shown in a comparative trial with a thicker snare [22] [23]. Thus, the apparently negative results in the study of Din et al. might simply be due to an underpowered sample rather than to nonsuperiority of the suction-based technique, and larger studies are needed.

Similarly to previous studies on cold polypectomy, the study by Din et al. has limitations. These are mainly related to the methodology adopted to assess the completeness of resection either at endoscopy or histology. As shown by the authors, the interobserver agreement for the endoscopic completeness of resection was only moderate, leaving uncertainty about the accuracy of the data, especially when it is considered that, as often occurs in endoscopic studies, the operator was not blinded to the randomized allocation. Similarly, it is questionable whether the pathologist could really detect a continuous lesion-free margin, on the very small histological sample especially bearing in mind the traumatization of the tissue resected with the suction-based technique. In addition, the study was performed at a center with special expertise in the field; therefore more data on the generalizability of the results are needed. The absolute prevalence of sessile serrated adenomas was also insufficient to allow any conclusion to be drawn on the efficacy of such a technique for this specific histotype, especially considering the poorly delineated margins of these lesions.

In conclusion, overall this study supports the widespread implementation of the cold snaring technique for diminutive lesions because of the technique’s outstanding efficacy and safety, especially when dedicated snares are used. Moreover, the suction pseudopolyp technique should be recommended, at least whenever the nonpolypoid shape of the lesion may prevent effective cold snaring, although it cannot be excluded that a more systematic use of the suction pseudopolyp technique might lead to even better clinical results.

• References

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