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Abstract and Introduction
Abstract
Background The impact of not referring sub-centimetre polyps identified at CT colonography upon the efficacy of colorectal cancer screening remains uncertain.
Aim To determine the distribution of advanced neoplasia according to polyp size in a screening setting.
Methods Published studies reporting the distribution of advanced adenomas in asymptomatic screening cohorts according to polyp size were identified by MEDLINE and EMBASE searches. Predefined outputs were the screening rates of advanced adenomas represented by diminutive (≤5 mm), small (6–9 mm), sub-centimetre (<10 mm) and large (≥10 mm) polyp sizes.
Results Data from four studies with 20 562 screening subjects met the primary inclusion criteria. Advanced adenomas were detected in 1155 (5.6%) subjects (95% CI = 5.3–5.9), corresponding to diminutive, small and large polyps in 4.6% (95% CI = 3.4–5.8), 7.9% (95% CI = 6.3–9.4) and 87.5% (95% CI = 86–89.4) of cases respectively. The frequency of advanced lesions among patients whose largest polyp was diminutive, small, sub-centimetre and large in size was 0.9%, 4.9%, 1.7% and 73.5% respectively.
Conclusions Based on this systematic review, a 6-mm polyp size threshold for polypectomy referral would identify over 95% of subjects with advanced adenomas, whereas a 10-mm threshold would identify 88% of cases.
Introduction
Colorectal cancer (CRC) screening aims to reduce CRC mortality through the identification of advanced neoplasia. In particular, effective CRC prevention has been closely related to the detection and removal of advanced adenomas, namely large adenomas (≥10 mm) or sub-centimetre adenomas with high-grade dysplasia (HGD) or a ≥25% villous component. The advent of less invasive but nontherapeutic tests for CRC screening, such as CT colonography (CTC) or capsule endoscopy, which may be highly accurate for detecting advanced neoplasia, has resulted into the need to determine appropriate size thresholds for post-test referral to polypectomy. In particular, it is widely accepted by the radiology community that only patients with polyps measuring ≥6 mm should be considered for colonoscopy referral following a CTC, and that this threshold could potentially be raised to 10-mm in some settings. Furthermore, the initial data on the accuracy of capsule endoscopy have been reported only for lesions ≥6 mm, suggesting that a similar threshold approach will be implemented.
To assess the consequences of not referring polyps below a certain size cut-off, nonreferral policy, previous studies have mainly focused on the individual or anecdotal risk of advanced neoplasia in subjects harbouring only small or diminutive polyps, generating concern for the validity of this policy. However, anecdotal risk does not necessarily correlate with the screening efficacy from a population perspective, which is more related to the overall burden of advanced neoplasia detected, but not with individual cases of sub-centimetre advanced neoplasia. If more individuals are being screened as a result of additional options, the benefit related to the increased detection of large adenomas and cancers should not be overlooked. As CRC screening realistically aims to reduce and not completely abolish CRC incidence or mortality, any effort that will improve the overall detection and removal of advanced neoplasia within a population should be balanced with the simplicity, acceptability, safety, cost-effectiveness and impact on overall compliance of a screening programme.
When assessing less invasive nontherapeutic approaches to CRC prevention, one key issue is the percentage of advanced neoplasia in a screening population that is confined to diminutive and small polyps. This is because screening efficacy can be largely assumed to be simply related to the rate of advanced neoplasia detection and removal, yet these sub-centimetre lesions may be left in place depending upon the sensitivity of the technique and the polyp size threshold that are employed. Ascertaining the true rate of advanced neoplasia according to polyp size would ideally be independent of detection technique, but must realistically be filtered through the accuracy of the final pathway common to all screening methods: optical colonoscopy. Fortunately, the performance of optical colonoscopy may be raised above its stand-alone baseline through the use of complementary data provided by CTC.
The aim of this systematic review was to assess the distribution of advanced neoplasia within average-risk screening populations according to polyp size to provide a reliable estimate on the potential loss of prevention efficacy by less-invasive nontherapeutic screening modalities associated with varying size thresholds for polypectomy referral.
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