Colonoscopy surveillance following adenoma removal to reduce the risk of colorectal cancer: a retrospective cohort study.

BACKGROUND

Colonoscopy surveillance is recommended for some patients post polypectomy. The 2002 UK surveillance guidelines classify post-polypectomy patients into low, intermediate and high risk, and recommend different strategies for each classification. Limited evidence supports these guidelines.

OBJECTIVES

To examine, for each risk group, long-term colorectal cancer incidence by baseline characteristics and the number of surveillance visits; the effects of interval length on detection rates of advanced adenomas and colorectal cancer at first surveillance; and the cost-effectiveness of surveillance compared with no surveillance.

DESIGN

A retrospective cohort study and economic evaluation.

SETTING

Seventeen NHS hospitals.

PARTICIPANTS

Patients with a colonoscopy and at least one adenoma at baseline.

MAIN OUTCOME MEASURES

Long-term colorectal cancer incidence after baseline and detection rates of advanced adenomas and colorectal cancer at first surveillance.

DATA SOURCES

Hospital databases, NHS Digital, the Office for National Statistics, National Services Scotland and Public Health England.

METHODS

Cox regression was used to compare colorectal cancer incidence in the presence and absence of surveillance and to identify colorectal cancer risk factors. Risk factors were used to stratify risk groups into higher- and lower-risk subgroups. We examined detection rates of advanced adenomas and colorectal cancer at first surveillance by interval length. Cost-effectiveness of surveillance compared with no surveillance was evaluated in terms of incremental costs per colorectal cancer prevented and per quality-adjusted life-year gained.

RESULTS

Our study included 28,972 patients, of whom 14,401 (50%), 11,852 (41%) and 2719 (9%) were classed as low, intermediate and high risk, respectively. The median follow-up time was 9.3 years. Colorectal cancer incidence was 140, 221 and 366 per 100,000 person-years among low-, intermediate- and high-risk patients, respectively. Attendance at one surveillance visit was associated with reduced colorectal cancer incidence among low-, intermediate- and high-risk patients [hazard ratios were 0.56 (95% confidence interval 0.39 to 0.80), 0.59 (95% confidence interval 0.43 to 0.81) and 0.49 (95% confidence interval 0.29 to 0.82), respectively]. Compared with the general population, colorectal cancer incidence without surveillance was similar among low-risk patients and higher among high-risk patients [standardised incidence ratios were 0.86 (95% confidence interval 0.73 to 1.02) and 1.91 (95% confidence interval 1.39 to 2.56), respectively]. For intermediate-risk patients, standardised incidence ratios differed for the lower- (0.70, 95% confidence interval 0.48 to 0.99) and higher-risk (1.46, 95% confidence interval 1.19 to 1.78) subgroups. In each risk group, incremental costs per colorectal cancer prevented and per quality-adjusted life-year gained with surveillance were lower for the higher-risk subgroup than for the lower-risk subgroup. Incremental costs per quality-adjusted life-year gained were lowest for the higher-risk subgroup of high-risk patients at £7821.

LIMITATIONS

The observational design means that we cannot assume that surveillance caused the reductions in cancer incidence. The fact that some cancer staging data were missing places uncertainty on our cost-effectiveness estimates.

CONCLUSIONS

Surveillance was associated with reduced colorectal cancer incidence in all risk groups. However, in low-risk patients and the lower-risk subgroup of intermediate-risk patients, colorectal cancer incidence was no higher than in the general population without surveillance, indicating that surveillance might not be necessary. Surveillance was most cost-effective for the higher-risk subgroup of high-risk patients.

FUTURE WORK

Studies should examine the clinical effectiveness and cost-effectiveness of post-polypectomy surveillance without prior classification of patients into risk groups.

TRIAL REGISTRATION

This trial is registered as ISRCTN15213649.

FUNDING

This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in

Bowel cancers develop from polyps, also called adenomas, which are growths on the lining of the bowel. Removal of adenomas, therefore, helps prevent bowel cancer. Adenomas can be detected and removed during colonoscopy, when a thin tube with a camera on one end is used to examine the bowel lining. In the UK, patients with adenomas are divided into three risk groups. Low-risk patients (i.e. those with one or two adenomas that are < 10 mm in size) are thought to be unlikely to develop bowel cancer after adenoma removal and follow-up colonoscopy is not recommended in this group. Intermediate-risk patients (i.e. those with three or four adenomas that are < 10 mm in size, or one or two adenomas with at least one ≥ 10 mm in size) are recommended to have another colonoscopy 3 years after adenoma removal. High-risk patients (i.e. those with five or more adenomas that are < 10 mm in size, or three or more adenomas with at least one ≥ 10 mm in size) are recommended to have another colonoscopy after 1 year and then usually again after 3 years. The number of follow-up colonoscopies carried out is stretching health-care resources and each procedure carries a small risk of complications for patients. It is possible that too many follow-up colonoscopies are being carried out. This study aimed to determine which patients require follow-up colonoscopies and how many are required to detect adenomas and prevent bowel cancer, while also being resource-efficient, cost-effective and not exposing patients to unnecessary risks. The study used data from 17 hospitals and cancer registries in the UK. In each risk group, one follow-up colonoscopy after adenoma removal was associated with a 40–50% reduction in bowel cancer risk. However, even without any follow-up, bowel cancer risk was no higher in some low- and intermediate-risk patients than in the general population. These patients may not need as many follow-up colonoscopies as recommended. In the case of higher-risk patients, who even after adenoma removal have a higher bowel cancer risk than the general population, follow-up colonoscopies are necessary and cost-effective.