Colon polyp surveillance – similar outcomes by size across the histology divide

With the integration of powerful imaging technology into screening colonoscopy practice, neoplastic polyps are increasingly detected and are being resected with greater frequency [1]. Increased polyp detection at screening leads to an ever-greater rate of patients who transition from screening protocols to “polyp surveillance” [2] [3]. Colonoscopy is resource-intensive and should be applied to those most likely to benefit in terms of colorectal cancer (CRC) morbidity and mortality reduction. In deciding how best to develop polyp surveillance protocols, two key questions should be kept in mind. First, who is at elevated risk based on their specific polyp burden; second, can colonoscopy surveillance reduce the risk for future CRC?

A Norwegian study analyzed CRC death rates in those with colonic adenoma at screening colonoscopy in comparison with the Norwegian population at large [4]. In aggregate, those with colorectal adenomas detected were at similar risk to the general population for future fatal CRC; however, when stratifying patients based on colon polyp characteristics, the standardized incidence mortality rate for CRC risk was decreased by 25% for those with small adenomas, but increased by 16% for those defined as being in the “high risk adenoma” cohort (based on polyp size and multiplicity). This study therefore showed a paradox in relation to the future risk of CRC in those with colonic adenomas. For those with a few small adenomas, the risk of fatal CRC was lower than the general public, but for those with high risk adenoma polyp features, future CRC risk was increased. A key limitation was the inability to further define the specific adenoma characteristics, such as advanced polyp size or multiplicity or both, within the high risk adenoma group that actually increased the CRC risk.

“The study shows that, at least for some polyp characteristics, in this case larger polyps, our approach to surveillance can be, if not the same, very similar across histologies.”

A UK study addressed to what extent colonoscopy surveillance of adenomas can reduce the risk of future CRC [5]. In the cohort of patients with one or two adenomas of ≥10 mm or three or four adenomas <10 mm in size, exposure to colonoscopy surveillance was associated with a 43% relative reduction in incident CRC risk in comparison to those who did not undergo polyp surveillance colonoscopy. Again a key limitation was the inability to further define the exact specific polyp characteristics (multiplicity and/or size) that led to the CRC risk reduction within the cohort. Conversely, those with a small adenoma without high grade features or a proximal polyp location had a standardized incidence ratio lower than that expected for the general population. Again, the paradox of surveillance patients in which certain polyp cohorts are at lower risk in comparison to the general population and other cohorts at elevated risk was apparent.

In the current volume of the journal, Zessner-Spitzenberg et al. followed over 383000 patients in Austria who underwent colonoscopy screening from 2010 to 2022, and then linked subsequent post-colonoscopy colorectal cancer (PCCRC) death rates from an Austrian national death registry database [6]. The authors assessed the association of PCCRC deaths with the diagnosis of different polyp histologies, including sessile serrated lesions (SSLs), adenomas, or hyperplastic polyps (HPPs), and further stratified analysis by polyp size ≥10 mm and <10 mm. The main outcome of these analyses was time to PCCRC death using a cause-specific Cox proportional hazards approach to associate polyp characteristics with time to PCCRC death. In the polyp surveillance cohort, they observed 329 deaths from PCCRC after follow-up of up to 13.0 years.

The authors found that the 10-year cumulative incidence of CRC death was essentially the same, at 0.24%, for those with adenomas detected as for those in the SSL cohort. Moreover, the CRC death rate in those with polyps, regardless of their histology, in aggregate was not significantly higher than for those with no neoplastic polyp detected. However, when analyzing only those patients with a polyp of ≥10 mm, the CRC death rates increased by between two- and five-fold, and this was true for all types of polyp histology. This relative increase in PCCRC rates in patients with polyps of ≥10 mm was present regardless of the histology of the polyp, including SSLs, HPPs, and adenomas that were ≥10 mm.

The authors then performed a sensitivity analysis looking at metachronous advanced neoplasia (MAN) in relation to the index polyp findings on screening colonoscopy. Similarly to the PCCRC end point findings, the initial detection at screening colonoscopy of a polyp sized ≥10 mm was associated with MAN and again this held true for all histologies (SSL, HPPs, and adenomas) ≥10 mm at similar relative frequencies in comparison with smaller polyps. In other words, the MAN findings trended similarly to the PCCRC outcomes, with size not histology being the key predictor of future advanced lesion risk.

In summary, this was a well-designed and welcome study that linked the risk of CRC death with well-defined polyp histology types and stratified by polyp size. The key findings show PCCRC outcomes were similar for the three histologic groups, all of which tracked with polyp size. If the screening colonoscopy revealed a polyp of ≥10 mm polyp, regardless of histology, this could be considered higher risk.

There are some limitations to the study. First, a multiplicity of small polyps was not accounted for. Second, the histology at screening may not have been representative in some larger lesions that, on surgical histology review, were actually CRC. Finally, colonoscopist lesion detection rate capabilities and other quality metrics were not described.

The study is in line with a Polish study that studied the correlation of CRC risk with adenoma characteristics and developed a risk classification system based on standardized incidence ratios. The authors found that polyps sized ≥20 mm or with high grade dysplasia were those that placed patients at highest risk [7]. In relation to specific guideline recommendations, the current study seems in line with those of the European Society for Gastrointestinal Endoscopy (ESGE), which recommends a 3-year surveillance interval for screening participants regardless of the histology, irrespective of subtype [3]. Other guidelines including the US Multi-Society Task Force (USMSTF) delineate surveillance intervals by histologic distinction (SSL versus HPP versus tubular adenoma) for polyps of ≥10 mm [2], although at least in this study the outcomes were quite similar.

A further emerging issue not addressed in this study is colonoscopy quality. Another Polish study correlated the adenoma detection rate at screening colonoscopy, as a marker of the quality of the colonoscopist, with CRC incidence and mortality [8]. The effect of the detection capabilities of the colonoscopist on future CRC incidence was evident across varying adenoma sizes, but was actually most pronounced in those with high risk adenomas. For those with high risk adenomas, the future CRC incidence was less than half in high adenoma-detecting colonoscopists in relation to low detectors.

The study by Zessner-Spitzenberg et al. is a useful contribution showing increased risk for fatal CRC associated with advanced polyp size ≥10 mm across different histologies. It did not show a CRC-associated risk for small sized polyps in comparison with the general population. These findings are in line with the ESGE recommendations, which have designated that patients with a few small polyps can be considered for “return to screening,” and do not undergo more intensive polyp surveillance protocols [3]. The study shows that, at least for some polyp characteristics, in this case larger polyps, our approach to surveillance can be, if not the same, very similar across histologies. The risk of CRC development is dependent on multiple factors, colonoscopy quality being one of them. As colonoscopy practice evolves, we will need to continue to critically assess the predictors of PCCRC and how and when to best intervene to reduce the risk for PCCRC.

Publication History

Article published online:
09 September 2024

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