Incomplete polyp resection – no simple solution

It has been estimated that incomplete adenoma resection is responsible for 10 % – 30 % of postcolonoscopy colorectal cancers (CRC) [1]. Several studies have shown that polyp removal is often incomplete, although data on polyps that are larger than diminutive are still limited [2] [3] [4] [5] [6] [7] [8]. A 10 % incomplete resection rate has been reported for neoplastic polyps of 5 – 20 mm [8]. Considering that complete resection is required to assure effective CRC screening and surveillance, three questions deserve attention.

• What is the incomplete resection rate for larger than diminutive polyps, both with hot and cold snare resection? We need additional data to understand the magnitude of the problem.

• What is the best method to measure incomplete resection? Obtaining marginal biopsies is impractical for clinical routine.

• How important, truly, is minute residual neoplasia? Current evidence that shows incomplete resection to be an important contributor to interval CRC remains circumstantial.

In the current issue of Endoscopy, Matsuura et al. [9] shed light on the first two questions. In a cross-sectional, single-center, multi-endoscopist study, they examined the incomplete resection rate using a cold snare of 307 diminutive and small adenomatous polyps ( ≤ 9 mm). After visibly complete polyp removal, the entire margin was removed by endoscopic mucosal resection. Incomplete resection was defined as the presence of neoplasia in the margin specimen. As the main result, the authors report an incomplete resection rate of 4 %. They also assessed, whether incomplete resection could be determined by examining the margin of the resected polyp. To their and probably the readers’ surprise, they found that the polyp margin could not be adequately examined in 206 or two-thirds of polyps, and the authors conclude that this approach is inadequate to assess incomplete resection.

The strengths of the study include the definition of incomplete resection, which was based on examining the entire defect margin after it was removed by mucosal resection. This has only been done in a few studies on diminutive polyps, and eliminates the risk of underestimating incomplete resection when relying on marginal biopsies [2] [4]. Although only performed at one center, a total of 11 endoscopists participated in the study, which makes the results more generalizable. Furthermore, the sample size is larger than many previous studies and the sample size is based on solid assumptions. One of the values of the study is that cold snare resection was used for polyps up to 9 mm. Although cold snare resection appears to be at least as safe and effective as hot snare resection for larger than diminutive polyps, this is not likely to have been adopted as standard clinical practice [7] [10] [11] [12] [13].

“These findings urge us to spend extra time examining the mucosal margin after resection.”

The study has several limitations. The authors point out that no dedicated cold snare was used, and it is possible that a different snare might have achieved a lower incomplete resection rate [7]. Furthermore, the authors assessed possible factors associated with incomplete resection in adjusted regression analysis and identified only female sex to be related to incomplete resection. However, there were only 12 incompletely resected polyps, which would not allow a reliable adjusted analysis of multiple factors. The wide confidence intervals around the point estimates therefore do not surprise. Where a numerical difference was apparent, a significant difference might not have been proven because of the low number of events. For instance, incomplete resection was (numerically) more frequent for larger than for smaller polyps, which is similar to previous reports [2] [3] [4] [8]. In addition, experts seemed to have a lower incomplete resection rate compared with senior residents, mirroring earlier findings that ability to achieve complete resection varies across endoscopists [8]. Along with the results on sex, location, and morphology, the results of the multivariate analysis cannot be generalized, and should be examined in larger studies.

What do we learn from this study? On the face of it, the incomplete resection rate appears to be low. But, when looking at the details, it may not be as low as it seems. For 6 – 9 mm polyps, the incomplete resection rate was 6 % – identical to the reported rate following hot snare resection [8]. This finding therefore does not support the idea that cold snare resection might improve completeness of resection over hot snare resection. It has been proposed that the different technique with cold resection (no need to lift the closed snare, therefore less risk of snare slippage) may provide a healthy resection margin and thereby facilitate completeness of resection [13]. Only a head-to-head comparison of cold and hot snare resection will provide a definitive answer on which method, if any, is superior.

Residual tissue was seen in 7 % of polyps after the initial resection. Marginal biopsies were only taken after visibly complete polyp removal. As part of the study one can expect that the margins were examined with scrutiny. This might not happen in clinical practice; a far higher incomplete resection rate, that includes visible and nonvisible residuals, might be expected in clinical practice. This study highlights the obvious – visual inspection leads to a substantial reduction in incomplete resection.

Perhaps one of the most surprising findings is that the polyp margin could not be adequately examined in 67 % of excised polyps. This high proportion of inadequate assessment is in contrast to studies that used the polyp margins to determine completeness of resection [6] [7]. Furthermore, in some countries it is common practice for the pathologist to provide a statement on the completeness of resection based on the excised polyp [14] [15]. If such evaluation is not possible for the majority of polyps, such practice is called into question. Some may argue – particularly our pathology colleagues – that preparation of the polyp specimen is key to allowing an adequate assessment of the polyp margin, and it is possible that differences in technique may affect histopathology assessment. Unfortunately, the authors did not provide details on polyp preparation.

Although the results of the study seem to dismiss the idea of using the polyp margins as an indicator for complete resection, this is probably premature. First, when using the inability of assessing the margin as an indicator for incomplete resection, the sensitivity was 0.92 with a negative predictive value of 99 % (calculated from the study data)! In other words, if the pathologist could assess the margin, complete polyp removal was highly likely. Of course, this may be particular to this study. These results should inspire further investigation into the question of whether histopathology examination of the polyp margin could reliably predict complete resection.

In summary, the study by Matsuura et al. adds valuable information on completeness of polyp resection using a cold snare. The incomplete resection rate for 1 – 9 mm polyps was 4 %, similar to previous reports on incomplete resection for diminutive and small polyps. Twice as many polyps had visible residual polyp tissue after initial polyp removal and required additional resection. These findings urge us to spend extra time examining the mucosal margin after resection. Pathology evaluation of the margin of the resected polyps was not possible for two-thirds of polyps, suggesting that this approach is not suitable to determine completeness of resection. However, it is not clear whether the observed inability to assess the margin is generalizable, as the histopathology method of polyp preparation may vary. Future large comparative effectiveness studies should be encouraged that assess efficacy of cold and hot snare resection, and identify a simple method to predict completeness of resection.

• References

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