Contribution of Surveillance Colonoscopy to Colorectal Cancer Prevention

Abstract

Background & aims: The contribution of surveillance colonoscopy, as opposed to that of initial colonoscopy examination, to prevention of colorectal cancer (CRC) is uncertain. We estimated the preventive effect of surveillance colonoscopy by applying the recently developed metric of adenoma dwell time avoided needed to prevent 1 CRC case (DTA).

Methods: We followed subjects in the prostate, lung, colorectal and ovarian (PLCO) cancer screening trial who underwent colonoscopies following positive findings from sigmoidoscopies (colonoscopy cohort, n = 15,935) for CRC incidence for 10 years. The number and timing of adenomas removed during surveillance were measured in a subset (n = 3492) of patients and extrapolated to the entire cohort to estimate the total avoided adenoma dwell time. A previously determined DTA value of 612 dwell years was applied to estimate the number of CRC cases prevented by surveillance. Proportional reduction in CRC was computed as CP/(CO+CP), where CO and CP are observed and estimated prevented cases, respectively.

Results: In the colonoscopy cohort of the PLCO, 2882 subjects had advanced adenomas (AAs), 572 had 3 or more non-advanced adenomas (NAA3+), 4496 had 1-2 non-advanced adenomas (NAA1-2), and 7985 had no adenoma (NA). The mean number of subsequent colonoscopy examinations over 10 years were 1.80 for subjects with AAs, 1.63 for subjects with NAA3+, and 1.46 for subjects with NAA1-2. Average years of avoided adenoma dwell time per subject were 4.0 for subjects with AAs, 5.5 for subjects with NAA3+, and 2.4 for subjects with NAA1-2. There were 56 cases of CRC in subjects with AAs, 4 cases of CRC in subjects with NAA3+, and 33 cases of CRC in subjects with NAA1-2. Estimated proportional reductions in CRC incidence were 25.0% in subjects with AAs (95% CI, 16%-34%), 34.4% in subjects with NAA1-2 (95% CI, 25%-40%), and 30.4% overall (in subjects with AAs, NAA3+, or NAA1-2; 95% CI, 25%-40%). Absolute CRC incidence reductions were 7.1 per 10,000 PY in subjects with AAs and 4.1 per 10,000 PY in subjects with NAA1-2.

Conclusions: Using the recently developed metric of DTA, we estimated that surveillance colonoscopy in the PLCO colonoscopy cohort during 10 years of follow up prevented 30% of CRC cases. Because the methodology for estimation is indirect, the true effect is uncertain.

Keywords: Colon Cancer; Progression; Screening; Tumor Precursor.

Conflict of interest statement

Conflicts of Interest: The authors report no conflicts.

Copyright © 2020 AGA Institute. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.. Flowchart of inclusion into PLCO colonoscopy cohort.

*SCU is the Study of Colonoscopy Utilization. Data on surveillance colonoscopy use and adenoma removal were available only from the SCU subset and were extrapolated to the remainder of the cohort. Numbers in brackets are size of SCU subset (e.g., 1304 for advanced adenoma). F/U is follow-up.

Figure 2:. Schematic of avoided dwell time.

Total time from all removed adenomas comprises the avoided adenoma dwell time for the given subject. For example, Subject 3 had an adenoma removed at year 3.5 and also at year 5.5; therefore, the total avoided dwell years equals 11 (10 − 3.5 + 10 − 5.5 ). Subjects with no adenomas removed during follow-up had a zero value for avoided dwell time.