Comparing the effectiveness of competing tests for reducing colorectal cancer mortality: a network meta-analysis

Comparing the effectiveness of competing tests for reducing colorectal cancer mortality: a network meta-analysis

ORIGINAL ARTICLE: Clinical Endoscopy Comparing the effectiveness of competing tests for reducing colorectal cancer mortality: a network meta-analysis...

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ORIGINAL ARTICLE: Clinical Endoscopy

Comparing the effectiveness of competing tests for reducing colorectal cancer mortality: a network meta-analysis B. Joseph Elmunzer, MD,1 Amit G. Singal, MSc, MD,2 Jeremy B. Sussman, MS, MD,3,4 Amar R. Deshpande, MD,5 Daniel A. Sussman, MSPH, MD,5 Marisa L. Conte, MLIS,6 Ben A. Dwamena, MD,7 Mary A.M. Rogers, PhD,4 Philip S. Schoenfeld, MSc (epi), MD,1,3 John M. Inadomi, MD,8 Sameer D. Saini, MS, MD,1,3 Akbar K. Waljee, MSc, MD1,3 Ann Arbor, Michigan, USA

Background: Comparative effectiveness data pertaining to competing colorectal cancer (CRC) screening tests do not exist but are necessary to guide clinical decision making and policy. Objective: To perform a comparative synthesis of clinical outcomes studies evaluating the effects of competing tests on CRC-related mortality. Design: Traditional and network meta-analyses. Two reviewers identified studies evaluating the effect of guaiacbased fecal occult blood testing (gFOBT), flexible sigmoidoscopy (FS), or colonoscopy on CRC-related mortality. Interventions: gFOBT, FS, colonoscopy. Main Outcome Measurements: Traditional meta-analysis was performed to produce pooled estimates of the effect of each modality on CRC mortality. Bayesian network meta-analysis (NMA) was performed to indirectly compare the effectiveness of screening modalities. Multiple sensitivity analyses were performed. Results: Traditional meta-analysis revealed that, compared with no intervention, colonoscopy reduced CRCrelated mortality by 57% (relative risk [RR] 0.43; 95% confidence interval [CI], 0.33-0.58), whereas FS reduced CRC-related mortality by 40% (RR 0.60; 95% CI, 0.45-0.78), and gFOBT reduced CRC-related mortality by 18% (RR 0.82; 95% CI, 0.76-0.88). NMA demonstrated nonsignificant trends favoring colonoscopy over FS (RR 0.71; 95% CI, 0.45-1.11) and FS over gFOBT (RR 0.74; 95% CI, 0.51-1.09) for reducing CRC-related deaths. NMAbased simulations, however, revealed that colonoscopy has a 94% probability of being the most effective test for reducing CRC mortality and a 99% probability of being most effective when the analysis is restricted to screening studies. Limitations: Randomized trials and observational studies were combined within the same analysis. Conclusion: Clinical outcomes studies demonstrate that gFOBT, FS, and colonoscopy are all effective in reducing CRC-related mortality. Network meta-analysis suggests that colonoscopy is the most effective test. (Gastrointest Endosc 2015;81:700-9.)

Abbreviations: CRC, colorectal cancer; EBGSG, Evidence-Based Gastroenterology Steering Group; FOBT, fecal occult blood testing; FS, flexible sigmoidoscopy; gFOBT, guaiac-based FOBT; NMA, network meta-analysis.

No funding bodies had any role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. All other authors disclosed no financial relationships relevant to this article.

DISCLOSURE: This study was supported in part by the following grants: National Institutes of Health (NIH) UL1RR024986 (B. Elmunzer), NIH K24DK080941 (J. Inadomi), NIH K24DK084208 (P. Schoenfeld), NIH U54CA163308 (A. Singal), Veterans Affairs Health Services Research & Development Career Development Awards (S. Saini 09-213, A. Waljee 11-217), VHA QUERI RRP 12-184 (S. Saini), and a Bankhead-Coley Team Science Program grant, 2BT02 (D. Sussman). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health, the U.S. Department of Veterans Affairs, or the Florida Department of Health.

Copyright ª 2015 by the American Society for Gastrointestinal Endoscopy 0016-5107/$36.00 http://dx.doi.org/10.1016/j.gie.2014.10.033

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Received July 12, 2014. Accepted October 24, 2014. Current affiliations: Department of Internal Medicine, Division of Gastroenterology and Hepatology, University of Michigan Health System,

(footnotes continued on last page of article)

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Colorectal cancer (CRC) is a leading, worldwide cause of cancer-related deaths.1,2 Although screening for CRC reduces the incidence and mortality of this malignancy,3,4 clinical outcomes studies directly comparing the effectiveness of competing screening tests are not available to guide clinical decision making or policy. Two randomized trials comparing colonoscopy with fecal immunohistochemical testing are ongoing; however, results may not be available for another decade or longer.5,6 There are currently no ongoing registered clinical outcomes trials comparing colonoscopy with flexible sigmoidoscopy (FS), CT colonography, or stool DNA testing. As a result, the optimal test remains uncertain, and national screening strategies vary. Fecal occult blood testing (FOBT) is used in most European countries,7 Canada,8 and Japan.9 In contrast, colonoscopydthe most invasive and costly modalitydis preferred in Germany, Poland, and the United States,7,10,11 despite the absence of comparative effectiveness data demonstrating its superiority. Colonoscopy may indeed be the most effective screening modality because it provides structural evaluation of the entire colon, detects both precancerous lesions and early prevalent cancers, and allows real-time polyp removal (thereby eliminating the risk of missing the lesion at follow-up examination). However, evidence of the comparative advantage of colonoscopy is necessary to justify its continued growth in this era of increasing screening acceptance12 but limited endoscopic capacity13 and rising health care expenditures.14 Because substantial clinical outcomes data are available for each test, and validated methodologies exist to indirectly compare the effectiveness of modalities, we used traditional and network meta-analysis to perform a comprehensive comparative appraisal of the effects of competing screening tests on CRC-related mortality. The results of this analysis may inform additional research in this field and supplement previously published decision analyses15,16 in guiding clinical decision making and screening policy.

Competing tests for colorectal cancer screening

sigmoidoscopy, endoscopy, FOBT, fecal immunohistochemical testing, and stool DNA testing. The search was augmented by manual searches of reference lists from potentially relevant articles to identify any additional studies that may have been missed by using the computer-assisted strategy. Additionally, all available guidelines, systematic reviews, and meta-analyses pertaining to CRC screening or individual screening modalities published after 2007 were identified through a manual search of the PubMed.gov database. These documents and their reference lists were reviewed for additional potentially relevant studies. The search was not limited by language.

Study selection Two investigators (B.J.E., A.K.W.) independently reviewed the titles of all identified citations to generate a list of potentially relevant articles. Abstract and brief manuscript review of articles with potentially relevant titles was then independently performed to select studies appropriate for our analysis. These studies were then reviewed in depth and the following eligibility criteria applied: (1) published manuscripts that examine the effect of colonoscopy, flexible sigmoidoscopy, stool-based CRC screening tests, CT colonography, or some combination thereof on the mortality of colorectal cancer; (2) studies that evaluate clinical outcomes in humans (not test performance characteristics); (3) studies in which data or patients are not duplicated in another manuscriptdfor randomized controlled trials (RCTs) and cohort studies that were longitudinally updated, only the most recent report was included; (4) studies with R5 years (mean) of follow-up (for trials and cohort studies); and (5) studies in which the number of events and total number of participants in each study group were reported. Articles reporting the effects of rigid sigmoidoscopy and barium enema were excluded because these are no longer accepted screening modalities.

METHODS Data extraction Data sources and search The study was conducted in accordance with the PRISMA and MOOSE statements.17,18 A research librarian designed and conducted a computer-assisted search by using the National Library of Medicine’s interface to PubMed/MEDLINE and Embase to identify potentially relevant articles. A search of human studies in these databases from inception through April 20, 2014 was performed by using controlled vocabulary descriptors (medical subject headings and Emtree) and keywords to represent the concepts of colorectal cancer, colon or rectal cancer, screening, and mortality. Results from this base search were combined with descriptors and keywords for various diagnostic procedures or screening methods including colonoscopy, colonography,

The following data were abstracted from each study in duplicate (B.J.E., A.G.S.) and independent fashion: first author, year of publication, country in which the study was conducted, screening modality or modalities evaluated, study methodology (trial, cohort study, case-control study, prospective vs retrospective), whether or not the study focused primarily on screening, follow-up duration, the number of events and total number of participants in the intervention and control groups (by using the intention-to-treat principle for trials), and the reported (adjusted) summary estimate (with confidence limits) of the intervention’s effect on overall CRC mortality or deaths related to CRC in the proximal or distal colon. Discrepancies in data extraction were resolved by consensus.

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Quality assessment

Sensitivity analyses

Two investigators (A.G.D., D.A.S.) critically appraised and quality rated all eligible studies by using 2 instruments. RCTs were assessed by criteria set forth by the EvidenceBased Gastroenterology Steering Group (EBGSG).19 These criteria were (1) concealed random allocation; (2) blinding of patients and caregivers; (3) equal use of cointerventions for the treatment and placebo groups; (4) complete followup of study patients; and (5) use of an intention-to-treat analysis. Observational studies were evaluated by using the Ottawa-Newcastle scale.20 This instrument rates observational studies on a 9-point scale based on the appropriateness of the study sample, comparability of study groups, and adequacy of assessing the exposure or outcome. Discrepancies in quality assessment also were resolved by consensus.

To assess the robustness of the results, several separate predefined traditional meta-analyses were repeated after (1) restricting to studies that concentrate primarily on CRC screening, (2) eliminating statistical heterogeneity by removing the minimum number of outlier studies for each screening modality, (3) restricting to studies that are prospective, (4) restricting to RCTs, (5) restricting to observational studies, (6) removing case-control studies, (7) restricting to studies with a low risk of bias based on an EBGSG score O2 (RCTs) or an Ottawa-Newcastle scale score R7 (observational studies), and (8) pooling the adjusted summary estimates and confidence limits reported in the studies (not the crude event rates used in the other analyses). In this last analysis, odds ratios (ORs) were assumed to approximate RR for this low probability outcome. In addition, NMAs were repeated for screening studies only and after we excluded the outlier studies responsible for statistical heterogeneity. To estimate the magnitude of superiority of the best test, we performed a threshold analysis by varying the RR of the best test toward the null in order to define the point at which it no longer ranks number 1 according to NMA-based rank probability analysis. Studies reporting the effect of a screening test on the mortality of CRC on the right or left side of the colon also were pooled by using traditional meta-analysis. Because crude event rates were not reported or calculable for these endpoints in many of the included studies, we used the reported summary estimates and CIs for this analysis. Again, ORs were assumed to approximate RR for this low probability outcome.

Data synthesis and analysis The outcome analyzed was mortality related to CRC. All primary analyses were performed by using crude event rates reported in, or derived from, each included study (ie, number of mortality events and total number of participants in the intervention and control groups). Pairwise comparisons of each screening modality versus no active intervention were performed by using traditional random-effects metaanalysis techniques in Stata 12.0 (StataCorp, College Station, Tex). The Cochran Q test and I2 inconsistency statistic were used to assess for statistical heterogeneity between trials. When heterogeneity was present, meta-influence analysis and Galbraith plot assessment were performed to identify responsible outlier studies. Pooled relative risks (RRs) and their 95% confidence intervals (CIs) were estimated for gFOBT, FS, and colonoscopy. To compare testing modalities, a hierarchical bayesian network meta-analysis (NMA) was performed with the GeMTC GUI statistical package.21 This form of metaanalysis generates estimates of effect sizes for all possible pairwise comparisons whether or not they have been evaluated in head-to-head trials. In particular, NMA allows indirect comparisons of colonoscopy versus FS, colonoscopy versus gFOBT, and FS versus gFOBT, based on each test’s effect relative to a common comparator (no intervention). These comparisons form the basis for a rank probability analysis of competing modalities, which uses simulations to determine the probability of any particular intervention being most effective. Posterior distributions were estimated by using Markov chain Monte Carlo simulations. A noninformative uniform prior distribution of effect sizes and precision was used. For each analysis, a series of 50,000 burn-in simulations was performed to allow convergence, and an additional 50,000 simulations were performed to produce the probability statements. Convergence of iterations was evaluated by using the Gelman-Rubin-Brooke statistic. Publication bias was assessed by using funnel plot asymmetry testing. 702 GASTROINTESTINAL ENDOSCOPY Volume 81, No. 3 : 2015

RESULTS Literature search A flow diagram depicting the search and selection process is provided in Figure 1. Initial searches of the Medline and Embase databases yielded 3704 citations. A manual search of the PubMed.gov database for pertinent systematic reviews, meta-analyses, and guidelines identified 19 summary documents (Appendix 1, available online at www. giejournal.org), review of which yielded 112 additional citations. Title review of these 2 groups of citations yielded 257 unique potentially relevant articles. Abstract and/or brief manuscript review of these articles yielded 60 manuscripts appropriate for detailed evaluation. Thirty of these were included in the final analysis. The remaining 30 articles (Appendix 2, available online at www.giejournal.org) were excluded because they did not meet eligibility criteria, detailed in the flow diagram. An article by Nishihara et al22 was excluded from the primary analysis because the number of events and total number of participants in each study group were not reported and could not be calculated from the original data set. However, the summary estimates www.giejournal.org

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Figure 1. Flow diagram depicting the article search and selection process. FS, flexible sigmoidoscopy.

reported in this study were included in a sensitivity analysis that pooled the adjusted summary estimates of included studies. There was 100% agreement between reviewers regarding final study selection.

Characteristics of included studies A summary of the clinical outcomes–based evidence supporting available CRC screening tests is presented in Table 1. The 30 studies meeting eligibility criteria are listed in Appendix 3, available online at www.giejournal.org. Characteristics of the studies included in the meta-analysis are listed in Table 2. The component studies included a total of 2,957,945 participants. No comparative effectiveness studies were identified; all component studies compared R1 screening test to no active intervention. Seventeen studies, made up of 1,230,485 participants, evaluated gFOBT. Of these, 4 were RCTs (329,642 patients), 1 was a quasiexperimental study (91,199), 3 were cohort studies (803,245 patients), and 9 were case-control studies (6399 patients). Seven studies, made up of 436,916 participants, evaluated FS. Of these, 4 were RCTs (414,966 participants), 1 was a quasiexperimental study (799 patients), and 2 were www.giejournal.org

case-control studies (21,151 patients). Eight studies, made up of 1,290,544 participants, evaluated colonoscopy. Of these, 5 were cohort studies (1,170,804 patients) and 3 were case-control studies (119,740 participants). No clinical outcomes studies evaluating CT colonography, fecal immunohistochemical testing, or fecal DNA were identified. Twenty-six studies (87%) focused primarily on screening, whereas the remainder enrolled participants with symptoms or known polyps or did not specifically restrict the analysis to asymptomatic, average-risk patients.

Testing for heterogeneity between eligible studies Pooled analysis of the effects of colonoscopy, FS, and gFOBT on the mortality of CRC demonstrated significant statistical heterogeneity among included studies for each modality (gFOBT I2 Z 50.1%; P Z .009; t2 Z .010; FS I2 Z 82.0%; P ! .001; t2 Z .091, and colonoscopy I2 Z 94.8%; P ! .001; t2 Z .11). Meta-influence analysis and visual inspection of Galbraith plots revealed that the following 5 outlier studies were responsible for the statistical heterogeneity: Lee 2007 (gFOBT), Muller 1995 (FS), Baxter 2009 Volume 81, No. 3 : 2015 GASTROINTESTINAL ENDOSCOPY 703

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TABLE 1. Characteristics of included studies Observational studies

Randomized trials

No. of studies

Participants

Magnitude of benefit

No. of trials

Participants

Magnitude of benefit

Colonoscopy

8

1,290,544

Highest

0

0

N/A

Sigmoidoscopy

3

21,950

High

4

414,966

High

Guaiac-based FOBT

13

900,843

Moderate

4

329,642

Moderate

CT colonography

0

0

N/A

0

0

N/A

FIT

0

0

N/A

0

0

N/A

Stool DNA test

0

0

N/A

0

0

N/A

N/A, Not applicable; FOBT, fecal occult blood testing; FIT, fecal immunohistochemical testing.

(colonoscopy), Singh 2010 (colonoscopy), and Baxter 2012 (colonoscopy). These studies were included in the basecase analysis but excluded in sensitivity analyses intended to eliminate statistical heterogeneity.

META-ANALYSIS RESULTS Compared with no intervention, traditional metaanalysis revealed that gFOBT resulted in an 18% reduction in CRC mortality (RR 0.82; 95% CI, 0.76-0.88). FS reduced CRC mortality by 40% (RR 0.60; 95% CI, 0.45-0.78), and colonoscopy reduced CRC mortality by 57% (RR 0.43; 95% CI, 0.33-0.58) (Fig. 2). Network meta-analysis revealed a non-statistically significant trend favoring colonoscopy over FS (RR 0.71; 95% CI, 0.45-1.11) and a non-statistically significant trend favoring FS over gFOBT (RR 0.74; 95% CI, 0.50-1.09) (Fig. 3). Colonoscopy was approximately 50% more effective than gFOBT for reducing CRC mortality (RR 0.53; 95% CI, 0.36-0.76) (Fig. 3). NMA-based rank probability analysis demonstrated that colonoscopy had a 94% probability of being the most effective test to reduce CRC mortality compared with FS (second rank probability of 87%) and gFOBT (third rank probability of 93%). In other words, a simulation-based analysis assimilating data from the evidence network revealed that colonoscopy was the most effective test in 94% of simulations (not the most effective test in only 6% of simulations), FS was the second most effective modality in 87% of simulations, and gFOBT was the third most effective test in 93% of simulations.

51% more effective than gFOBT (RR 0.49; 95% CI, 0.300.76). Repeat NMA after we removed outlier studies revealed that colonoscopy may be 68% more effective than FS (RR 0.32; 95% CrI, 0.23-0.45) and 72% more effective than gFOBT (RR 0.28; 95% CrI, 0.21-0.37). In these sensitivity analyses, rank probability testing demonstrated that colonoscopy had a 99% to 100% probability of being the most effective test for reducing CRC mortality. NMA-based threshold analysis revealed that colonoscopy would remain the best test (first rank probability 51%) even if its absolute effectiveness compared with no intervention were 16% lower than observed in the primary analysis. Four gFOBT studies, 5 FS studies, and 5 colonoscopy studies specifically reported the impact of an intervention on left-sided and right-sided CRC mortality. Subgroup analysis of these studies revealed that (1) gFOBT is equally effective in reducing left-sided (RR 0.89; 95% CI, 0.771.01) and right-sided (RR 0.87; 95% CI, 0.75-0.99) CRC mortality, (2) FS is significantly effective in the left side of the colon (RR 0.41; 95% CI, 0.21-0.61) but does not appear to impact right-sided CRC mortality (RR 0.89; 95% CI, 0.691.09), and (3) colonoscopy significantly reduces CRC mortality in the left side of the colon (RR 0.27; 95% CI, 0.15-0.40) and demonstrates a strong trend toward benefit in the right side of the colon (RR 0.74; 95% CI, 0.47-1.02).

Publication bias The funnel plot asymmetry test for publication bias was negative by using both the Harbord test (P Z .615) and the Peters test (P Z .79).

DISCUSSION SENSITIVITY ANALYSES Predefined sensitivity analyses by using traditional metaanalysis did not significantly change the overall findings (Fig. 4). Repeat NMA after we restricted analysis to screening studies revealed that colonoscopy may be 44% more effective than FS (RR 0.56; 95% CI, 0.32-0.94) and

This pooled analysis of available clinical outcomes data demonstrates that, when compared with no intervention, colonoscopy reduces CRC mortality by 57% compared with a 40% reduction associated with FS and an 18% reduction associated with gFOBT. NMA-based indirect comparisons show that colonoscopy has a very high likelihood

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TABLE 2. Characteristics of included studies

Study

Country

Modality

Design

Sample size

Follow-up, y

Patient age, y

Screening, yes/no

Quality score*

Jorgensen 2002

Denmark

FOBT

RCT

61,933

13

45-75

Yes

1/5

Lindholm 2008

Sweden

FOBT

RCT

68,308

9

60-64

Yes

3/5

Scholefield 2012

UK

FOBT

RCT

152,850

19.5

45-74

Yes

2/5

Shaukat 2013

U.S.

FOBT

RCT

46,551

30

50-80

Yes

2/5

France

FOBT

Quasi-experiment

91,199

11

45-74

Yes

8/9

Lee 2007

S. Korea

FOBT

Cohort

42,150

13.1

40-59

Yes

7/9

Malila 2007

Finland

FOBT

Cohort

1785

19.9

50-63

Yes

5/9

Libby 2012

UK

FOBT

Cohort

759,310

3-10

50-69

Yes

7/9

Newcomb 1992,y

U.S.

FOBT

Case-control

262

N/A

Not reported

Yes

7/9

Japan

FOBT

Case-control

112

N/A

Not reported

Yes

8/9

Selby 1993

U.S.

FOBT

Case-control

1213

N/A

O50

Yes

8/9

Lazovich 1995

U.S.

FOBT

Case-control

693

N/A

40-84

Yes

9/9

Saito 1995

Japan

FOBT

Case-control

770

N/A

40-79

Yes

9/9

Zappa 1997

Italy

FOBT

Case-control

1236

N/A

O41

Yes

6/9

Bertario 1999

Italy

FOBT

Case-control

570

N/A

O40

Yes

7/9

France

FOBT

Case-control

890

N/A

45-80

Yes

7/9

U.S.

FOBT

Case-control

653

N/A

O45

Yes

9/9

Hoff 2009

Norway

FS

RCT

55,736

6

55-64

Yes

3/5

Atkin 2010

UK

FS

RCT

170,038

11.2

55-64

Yes

4/5

Segnan 2011

Italy

FS

RCT

34,292

11.4

55-64

Yes

3/5

Schoen 2012

U.S.

FS

RCT

154,900

11.9

55-74

Yes

4/5

Thiis-Evensen 1999

Norway

FS

Quasi-experiment

799

13

50-99

Yes

5/9

Newcomb 1992,y

U.S.

FS

Case-control

262

N/A

Not reported

Yes

7/9

Muller 1995,y

U.S.

FS

Case-control

20,889

N/A

69 (mean)

No

8/9

Kahi 2009

U.S.

Colonoscopy

Cohort

715

8

50-86

Yes

8/9

Singh 2010

Canada

Colonoscopy

Cohort

54,803

5.7

50-80

Yes

7/9

Jacob 2012

Canada

Colonoscopy

Cohort

1,089,998

5-9

50-74

Yes

8/9

Manser 2012

Switzerland

Colonoscopy

Cohort

22,686

6

50-80

Yes

6/9

Zauber 2012

U.S.

Colonoscopy

Cohort

2602

15.8

62 (mean)

No

6/9

Muller 1995 y

U.S.

Colonoscopy

Case-control

20,889

N/A

69 (mean)

No

8/9

Baxter 2009

Canada

Colonoscopy

Case-control

61,752

N/A

52-90

No

6/9

Baxter 2012

U.S.

Colonoscopy

Case-control

37,099

N/A

70-89

No

6/9

Faivre 2004

Hiwatashi 1993

Faivre 1999 Scheitel 1999

,

FOBT, Fecal occult blood testing; RCT, randomized controlled trial; UK, United Kingdom; U.S., United States; N/A, not applicable; FS, flexible sigmoidoscopy. *RCTs rated on a 5-point scale; observational studies rated on a 9-point scale. yStudies evaluating O1 modality.

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Figure 2. Meta-analysis of the effect of screening tests compared with no intervention on colorectal cancer mortality. FOBT, fecal occult blood testing; RR, relative risk; CI, confidence interval.

of being the best modality for reducing CRC-related deaths. These findings remained consistent in multiple sensitivity analyses. To create the most comprehensive and robust evidence network, we evaluated all available clinical outcomes studies in this NMA, including 4 studies that did not focus primarily on screening. Thus, the results of our primary analysis must be extrapolated to a certain extent to the screening context. However, a sensitivity analysis restricted to the 26 screening studies did not substantively change the overall results and, in fact, increased the relative effectiveness of colonoscopy compared with the other modalities. Current screening recommendations are based primarily on simulation-driven decision analyses, which suggest that annual FOBT, FS every 5 years (with mid-interval FOBT), and colonoscopy every 10 years are equivalent in reducing CRC mortality.15,16 These analyses, however, which do not

consider clinical outcomes data, assume 100% compliance to screening, follow-up testing, and surveillance of patients with adenomasdrates much higher than expected in usual clinical practice.23,24 In contrast, the estimates of effectiveness for each screening modality produced by this metaanalysis are based on empiric investigational data and are more likely to reflect important real-world factors such as suboptimal participation. Because colonoscopy is less sensitive than FOBT and FS to variations in patient compliance15 and has better performance characteristics, the comparative superiority of colonoscopy demonstrated in this meta-analysis seems quite plausible. Certainly, other considerations such as cost, safety, acceptability, and availability are integral in determining the most appropriate screening strategy for any particular population. Although this NMA suggests that colonoscopy is the most effective test, it is also the most invasive of all

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Figure 3. Evidence network of the effect of screening options on colorectal cancer mortality. Traditional meta-analysis–generated direct comparisons are denoted by solid lines, and network meta-analysis–generated indirect comparisons are denoted by dashed lines. Direction of the arrow denotes superiority. gFOBT, guaiac-based fecal occult blood testing.

screening modalities, requires a full bowel preparation and systemic sedation, and generally results in loss of wages or other productivity for the patient and escort on the day of the procedure. Further, some patients may favor other screening tests on the basis of psychosocial or cultural factors. Therefore, promoting colonoscopy as the preferred option in all contexts may be counterproductive, especially because offering patients a choice of CRC screening tests has been shown to increase compliance.25 Pooled estimates from the limited number of included studies that evaluated the impact of screening interventions on CRC outcomes in the left and right sides of the colon are consistent with prior reports suggesting that colonoscopy is less effective in the proximal colon than it is distally.26-28 This observation may be related to nonmodifiable factors such as the biology of right-sided neoplasms (more aggressive progression).29,30 However, addressable deficiencies in colonoscopy performance, such as preparation quality in the proximal colon, the recognition of subtle right-sided polyps, and the completeness of polypectomy are probably relevant and merit continued attention.31,32 Additional research focused on increasing the detection of serrated lesions in the right side of the colon through education and training33 and advances in wide-field imaging34,35 or molecular targeting36 may be of significant value. The results of this study should be interpreted in the context of several important limitations. First, all colonoscopy studies included in this comparative analysis were observational in nature, potentially exaggerating the relative effectiveness of this modality. This may occur because of differential confounding in favor of colonoscopy and because cohort and case control study results are based on 100% compliance in the intervention group, whereas intention-to-screen results of RCTs (representing the

majority of included FS and gFOBT data) are compromised by noncompliance. Indeed, the analyses we performed that were restricted to RCTs of FOBT and FS demonstrated 3% to 12% lower risk reduction compared with overall meta-analysis results (which include observational studies). Therefore, colonoscopy RCTs may yield estimates of benefit that are more conservative than those observed in this study. However, the threshold analysis we performed revealed that colonoscopy could be up to 16% less effective than observed in this meta-analysis and still remain the most effective modality for reducing CRCrelated mortality. Additionally, it is not clearly established that noncompliance to colonoscopy in clinical practice would be substantially higher than to FS (as evidenced by comparing the attendance rates in some published FS RCTs37 and the first interim report of a large colonoscopy RCT5) or to stool-based testing, which requires annual or biennial participation for O2 decades and attendance of follow-up colonoscopies. Along these lines, performing a fully comprehensive comparative appraisal of the CRC screening literature necessitated combining randomized trials and observational studies within the same meta-analysis. The validity of combining observational and experimental data in the same synthesis has been questioned, but cogent methodologic arguments in favor of this approach exist,38 especially when RCT data alone are insufficient to answer the clinical question.38,39 Furthermore, RCTs with long follow-up (such as CRC screening trials) demonstrate characteristics similar to observational studies because of post-randomization confounding,40 providing support to the strategy of combining observational and experimental data in our analysis. Second, the included observational studies, particularly the case-control studies, often adjusted for imbalances in

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Finally, because clinical outcomes data exist for gFOBT only, this NMA did not include studies of the more sensitive immunohistochemical41 or DNA tests,42 potentially biasing the results against stool-based screening. Based on favorable performance characteristics, most formal screening programs have abandoned gFOBT in favor of fecal immunohistochemical testing; however, understanding the comparative effectiveness of gFOBT remains of clinical importance because this test is still used routinely or sporadically in some countries, including the United Kingdom, Canada, and the United States. Furthermore, gFOBT studies represent the foundation for the evidence base in support of stool testing. Although this comparative appraisal suggests that colonoscopy is the most effective test, it also highlights the phenomenon that colonoscopy has gained widespread acceptance in several parts of the world without the support of a single randomized trial. This intensifies the importance of ongoing comparative effectiveness trials of colonoscopy versus fecal immunohistochemical testing5,6,43 but also emphasizes the need for trials comparing colonoscopy to FS, which has developed a very strong evidence base. Although we are awaiting RCT results, this network meta-analysis along with previously published cost-effectiveness analyses44,45 may support certain countries’ commitment to colonoscopy as the primary CRC screening strategy. Other public health organizations may use the results of this NMA as one factor in determining the most appropriate screening test for their patient population. In conclusion, FOBT, FS, and colonoscopy are all effective in preventing CRC deaths. Within the limitations of comparing the higher quality evidence supporting FOBT and FS with the observational data on colonoscopy, NMA suggests that colonoscopy is the most effective test for preventing CRC deaths. REFERENCES

Figure 4. Sensitivity analyses for each screening modality compared with no intervention. FOBT, fecal occult blood testing; RCT, randomized controlled trial; RR, relative risk; FS, flexible sigmoidoscopy.

patient characteristics that could affect the risk of CRC. This adjustment was lost in our primary analysis because we used crude event rates to calculate RRs, potentially biasing in favor of one screening intervention over the others. However, a sensitivity analysis pooling the reported adjusted summary estimates and confidence limits (rather than crude event rates) did not differ from the primary analysis. 708 GASTROINTESTINAL ENDOSCOPY Volume 81, No. 3 : 2015

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Competing tests for colorectal cancer screening 31. Cohen LB. Split dosing of bowel preparations for colonoscopy: an analysis of its efficacy, safety, and tolerability. Gastrointest Endosc 2010;72: 406-12. 32. Pohl H, Srivastava A, Bensen SP, et al. Incomplete polyp resection during colonoscopy-results of the complete adenoma resection (CARE) study. Gastroenterology 2013;144:74-80.e1. 33. Coe SG, Crook JE, Diehl NN, et al. An endoscopic quality improvement program improves detection of colorectal adenomas. Am J Gastroenterol 2013;108:219-26; quiz 27. 34. Pohl J, Schneider A, Vogell H, et al. Pancolonic chromoendoscopy with indigo carmine versus standard colonoscopy for detection of neoplastic lesions: a randomised two-centre trial. Gut 2011;60: 485-90. 35. Gross SA, Buchner AM, Crook JE, et al. A comparison of high definitionimage enhanced colonoscopy and standard white-light colonoscopy for colorectal polyp detection. Endoscopy 2011;43:1045-51. 36. Liu Z, Miller SJ, Joshi BP, et al. In vivo targeting of colonic dysplasia on fluorescence endoscopy with near-infrared octapeptide. Gut 2013;62: 395-403. 37. Segnan N, Armaroli P, Bonelli L, et al. Once-only sigmoidoscopy in colorectal cancer screening: follow-up findings of the Italian Randomized Controlled TrialdSCORE. J Natl Cancer Inst 2011;103: 1310-22. 38. Shrier I, Boivin JF, Steele RJ, et al. Should meta-analyses of interventions include observational studies in addition to randomized controlled trials? A critical examination of underlying principles. Am J Epidemiol 2007;166:1203-9. 39. Golder S, Loke YK, Bland M. Meta-analyses of adverse effects data derived from randomised controlled trials as compared to observational studies: methodological overview. PLoS Med 2011;8: e1001026. 40. Hernan MA, Hernandez-Diaz S, Robins JM. Randomized trials analyzed as observational studies. Ann Intern Med 2013;159:560-2. 41. Allison JE, Tekawa IS, Ransom LJ, et al. A comparison of fecal occultblood tests for colorectal-cancer screening. N Engl J Med 1996;334: 155-9. 42. Imperiale TF, Ransohoff DF, Itzkowitz SH, et al. Multitarget stool DNA testing for colorectal-cancer screening. N Engl J Med 2014;370: 1287-97. 43. Kaminski MF, Bretthauer M, Zauber AG, et al. The NordICC Study: rationale and design of a randomized trial on colonoscopy screening for colorectal cancer. Endoscopy 2012;44:695-702. 44. Sonnenberg A, Delco F, Inadomi JM. Cost-effectiveness of colonoscopy in screening for colorectal cancer. Ann Intern Med 2000;133:573-84. 45. Vijan S, Hwang EW, Hofer TP, et al. Which colon cancer screening test? A comparison of costs, effectiveness, and compliance. Am J Med 2001;111:593-601.

Ann Arbor, Michigan (1), Department of Internal Medicine, Division of Digestive and Liver Diseases and the Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas (2), Center for Clinical Management Research, Ann Arbor Veterans Affairs Healthcare System (3), Department of Internal Medicine, Division of General Internal Medicine, University of Michigan Health System, Ann Arbor, Michigan (4), Department of Internal Medicine, Division of Gastroenterology, University of Miami Miller School of Medicine, Miami, Florida (5), University of Michigan School of Medicine (6), Department of Radiology, Division of Nuclear Medicine, University of Michigan Health System, Ann Arbor, Michigan (7), Department of Medicine, Division of Gastroenterology, University of Washington School of Medicine, Seattle, Washington, USA (8). *Reprint requests: B. Joseph Elmunzer, MD, University of Michigan Medical Center, 3912 Taubman Center, Ann Arbor, MI 48109. If you would like to chat with an author of this article, you may contact Dr Elmunzer at [email protected].

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APPENDIX 1. SYSTEMATIC REVIEWS, META-ANALYSES, AND GUIDLEINES USED IN LITERATURE SEARCH Brenner H, Stock C, Hoffmeister M. Effect of screening sigmoidoscopy and screening colonoscopy on colorectal cancer incidence and mortality: systematic review and meta-analysis of randomised controlled trials and observational studies. BMJ 2014;348:g2467. Holme Ø, Bretthauer M, Fretheim A, et al. Flexible sigmoidoscopy versus faecal occult blood testing for colorectal cancer screening in asymptomatic individuals. Cochrane Database Syst Rev 2013;(9):CD009259. http://dx.doi.org/10.1002/14651858.CD009259.pub2. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2008;149:627-37. Levin B, Lieberman DA, McFarland B, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology 2008;134:1570-95. Rex DK, Johnson DA, Anderson JC, et al. American College of Gastroenterology guidelines for colorectal cancer screening 2009 [corrected]. Am J Gastroenterol 2009;104:739-50. Qaseem A, Denberg TD, Hopkins RH Jr, et al. Screening for colorectal cancer: a guidance statement from the American College of Physicians. Ann Intern Med 2012;156:378-86. Littlejohn C, Hilton S, Macfarlane GJ, et al. Systematic review and meta-analysis of the evidence for flexible sigmoidoscopy as a screening method for the prevention of colorectal cancer. Br J Surg 2012;99:1488-500. Elmunzer BJ, Hayward RA, Schoenfeld PS, et al. Effect of flexible sigmoidoscopy-based screening on incidence and mortality of colorectal cancer: a systematic review and meta-analysis of randomized controlled trials. PLoS Med 2012;9:e1001352. Burt RW, Barthel JS, Dunn KB, et al. NCCN clinical practice guidelines in oncology. Colorectal cancer screening. J Natl Compr Canc Netw 2010;8:8-61.

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Elmunzer et al Chaparro M, Gisbert JP, Del Campo L, et al. Accuracy of computed tomographic colonography for the detection of polyps and colorectal tumors: a systematic review and meta-analysis. Digestion 2009;80:1-17. de Haan MC, van Gelder RE, Graser A, et al. Diagnostic value of CT-colonography as compared to colonoscopy in an asymptomatic screening population: a meta-analysis. Eur Radiol 2011;21:1747-63. Haug U, Knudsen AB, Brenner H, et al. Is fecal occult blood testing more sensitive for left- versus right-sided colorectal neoplasia? A systematic literature review. Expert Rev Mol Diagn 2011;11:605-16. Lee BI, Hong SP, Kim SE, et al. Korean guidelines for colorectal cancer screening and polyp detection. Clin Endosc 2012;45:25-43. Pickhardt PJ, Hassan C, Halligan S, et al. Colorectal cancer: CT colonography and colonoscopy for detectiondsystematic review and meta-analysis. Radiology 2011;259:393-405. Winawer SJ, Krabshuis J, Lambert R, et al. Cascade colorectal cancer screening guidelines: a global conceptual model. J Clin Gastroenterol 2011;45:297-300. Whitlock EP, Lin JS, Liles E, et al. Screening for colorectal cancer: a targeted, updated systematic review for the U.S. Preventive Services Task Force. Ann Intern Med 2008;149:638-58. McFarland EG, Levin B, Lieberman DA, et al. Revised colorectal screening guidelines: joint effort of the American Cancer Society, U.S. Multisociety Task Force on Colorectal Cancer, and American College of Radiology. Radiology 2008;248:717-20. Niv Y, Hazazi R, Levi Z, et al. Screening colonoscopy for colorectal cancer in asymptomatic people: a meta-analysis. Dig Dis Sci 2008;53:3049-54. Hewitson P, Glasziou P, Watson E, et al. Cochrane systematic review of colorectal cancer screening using the fecal occult blood test (hemoccult): an update. Am J Gastroenterol 2008;103:1541-9. National Cancer Institute Colorectal Cancer Screening Physician Data Query. Available at: http://www.cancer.gov/cancertopics/pdq/screening/ colorectal/HealthProfessional/page1/AllPages/Print. Accessed March 11, 2013.

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APPENDIX 2. STUDIES EXCLUDED AFTER FULL MANUSCRIPT REVIEW Hardcastle JD, Chamberlain JO, Robinson MH, et al. Randomised controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet 1996;348:1472-7. Singh H, Turner D, Xue L, et al. Risk of developing colorectal cancer following a negative colonoscopy examination: evidence for a 10-year interval between colonoscopies. JAMA 2006;295:2366-73. Kronborg O, Jorgensen OD, Fenger C, et al. Randomized study of biennial screening with a faecal occult blood test: results after nine screening rounds. Scand J Gastroenterol 2004;39:846-51. Mandel JS, Bond JH, Church TR, et al. Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study. N Engl J Med 1993;328:1365-71. Brenner H, Chang-Claude J, Seiler CM, et al. Potential for colorectal cancer prevention of sigmoidoscopy versus colonoscopy: population-based case control study. Cancer Epidemiol Biomarkers Prev 2007;16:494-9. Selby JV, Friedman GD, Quesenberry CP Jr, et al. A case-control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med 1992;326:653-7. Atkin WS, Morson BC, Cuzick J. Long-term risk of colorectal cancer after excision of rectosigmoid adenomas. N Engl J Med 1992;326: 658-62. Brenner H, Chang-Claude J, Seiler CM, et al. Does a negative screening colonoscopy ever need to be repeated? Gut 2006;55:1145-50. Brenner H, Arndt V, Sturmer T, et al. Long-lasting reduction of risk of colorectal cancer following screening endoscopy. Br J Cancer 2001;85:972-6. Nishida HU, Urano S. Effectiveness of repeated screening using the fecal occult blood test and its impact on reducing false-negative cancer cases. Eur J Cancer Prev 2011;20:184-9. Winawer SJ, Flehinger BJ, Schottenfeld D, et al. Screening for colorectal cancer with fecal occult blood testing and sigmoidoscopy. J Natl Cancer Inst 1993;85:1311-8. Whynes DK, Mangham CM, Balfour TW, et al. Analysis of deaths occurring within the Nottingham trial of faecal occult blood screening for colorectal cancer. Gut 2010;59:1088-93. Hardcastle JD, Thomas WM, Chamberlain J, et al. Randomised, controlled trial of faecal occult blood screening for colorectal cancer. Results for first 107,349 subjects. Lancet 1989;1:1160-4. Meagher AP, Stuart M. Does colonoscopic polypectomy reduce the incidence of colorectal carcinoma? Aust N Z J Surg 1994;64:400-4. Nakama H. A study on the efficacy of a screening program for colorectal cancer in a small Japanese village. Clin Investig 1994;72:117-21.

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Competing tests for colorectal cancer screening Murakami R, Tsukuma H, Kanamori S, et al. Natural history of colorectal polyps and the effect of polypectomy on occurrence of subsequent cancer. Int J Cancer 1990;46:159-64. Saito H, Soma Y, Nakajima M, et al. A case-control study evaluating occult blood screening for colorectal cancer with hemoccult test and an immunochemical hemagglutination test. Oncol Rep 2000;7:815-9. Kewenter J, Brevinge H, Engaras B, et al. Results of screening, rescreening, and follow-up in a prospective randomized study for detection of colorectal cancer by fecal occult blood testing. Results for 68,308 subjects. Scand J Gastroenterol 1994;29:468-73. Mandel JS, Church TR, Ederer F, et al. Colorectal cancer mortality: effectiveness of biennial screening for fecal occult blood. J Natl Cancer Inst 1999;91:434-7. Slattery ML, Edwards SL, Ma KN, et al. Colon cancer screening, lifestyle, and risk of colon cancer. Cancer Causes Control 2000;11:555-63. Bleiberg H, Autier P, Huet F, et al. Colorectal cancer (CRC) screening using sigmoidoscopy followed by colonoscopy: a feasibility and efficacy study on a cancer institute based population. Ann Oncol 2006;17:1328-32. Blom J, Yin L, Liden A, et al. A 9-year follow-up study of participants and nonparticipants in sigmoidoscopy screening: importance of self-selection. Cancer Epidemiol Biomarkers Prev 2008;17:1163-8. Rabeneck L, Lewis JD, Paszat LF, et al. Risk of proximal and distal colorectal cancer following flexible sigmoidoscopy: a population-based cohort study. Am J Gastroenterol 2008;103:2075-82. Muller AD, Sonnenberg A. Prevention of colorectal cancer by flexible endoscopy and polypectomy: a case-control study of 32,702 veterans. Ann Intern Med 1995;123:904-10. Newcomb PA, Storer BE, Morimoto LM, et al. Long-term efficacy of sigmoidoscopy in the reduction of colorectal cancer incidence. J Natl Cancer Inst 2003;95:622-5. Mulder SA, van Soest EM, Dieleman JP, et al. Exposure to colorectal examinations before a colorectal cancer diagnosis: a case-control study. Eur J Gastroenterol Hepatol 2010;22:437-43. Winawer SJ, Zauber AG, Ho MN, et al. Prevention of colorectal cancer by colonoscopic polypectomy. The National Polyp Study Workgroup. N Engl J Med 1993;329:1977-81. Citarda F, Tomaselli G, Capocaccia R, et al. Efficacy in standard clinical practice of colonoscopic polypectomy in reducing colorectal cancer incidence. Gut 2001;48:812-5. Brenner H, Chang-Claude J, Seiler CM, et al. Protection from colorectal cancer after colonoscopy: a population-based, case-control study. Ann Intern Med 2011;154:22-30. Nishihara R, Wu K, Lochhead P, et al. Long-term colorectal-cancer incidence and mortality after lower endoscopy. N Engl J Med 2013;369: 1095-105.

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APPENDIX 3. INCLUDED STUDIES Jorgensen OD, Kronborg O, Fenger C. A randomised study of screening for colorectal cancer using faecal occult blood testing: results after 13 years and seven biennial screening rounds. Gut 2002;50:29-32. Lindholm E, Brevinge H, Haglind E. Survival benefit in a randomized clinical trial of faecal occult blood screening for colorectal cancer. Br J Surg 2008;95:1029-36. Scholefield JH, Moss SM, Mangham CM, et al. Nottingham trial of faecal occult blood testing for colorectal cancer: a 20-year follow-up. Gut 2012;61:1036-40. Faivre J, Dancourt V, Lejeune C, et al. Reduction in colorectal cancer mortality by fecal occult blood screening in a French controlled study. Gastroenterology 2004;126:1674-80. Lee KJ, Inoue M, Otani T, et al. Colorectal cancer screening using fecal occult blood test and subsequent risk of colorectal cancer: a prospective cohort study in Japan. Cancer Detect Prev 2007;31:3-11. Malila N, Hakama M, Pukkala E. A 25-year follow-up of a population screened with faecal occult blood test in Finland. Acta Oncol 2007;46:1103-6. Libby G, Brewster DH, McClements PL, et al. The impact of population-based faecal occult blood test screening on colorectal cancer mortality: a matched cohort study. Br J Cancer 2012;107:255-9. Newcomb PA, Norfleet RG, Storer BE, et al. Screening sigmoidoscopy and colorectal cancer mortality. J Natl Cancer Inst 1992;84:1572-5. Hiwatashi N, Morimoto T, Fukao A, et al. An evaluation of mass screening using fecal occult blood test for colorectal cancer in Japan: a case-control study. Jpn J Cancer Res 1993;84:1110-2. Selby JV, Friedman GD, Quesenberry CP Jr, et al. Effect of fecal occult blood testing on mortality from colorectal cancer: a case-control study. Ann Intern Med 1993;118:1-6. Lazovich D, Weiss NS, Stevens NG, et al. A case-control study to evaluate efficacy of screening for faecal occult blood. J Med Screen 1995;2:84-9. Saito H, Soma Y, Koeda J, et al. Reduction in risk of mortality from colorectal cancer by fecal occult blood screening with immunochemical hemagglutination test: a case-control study. Int J Cancer 1995;61:465-9. Zappa M, Castiglione G, Grazzini G, et al. Effect of faecal occult blood testing on colorectal mortality: results of a population-based case-control study in the district of Florence, Italy. Int J Cancer 1997;73: 208-10. Bertario L, Russo A, Crosignani P, et al. Reducing colorectal cancer mortality by repeated faecal occult blood test: a nested case-control study. Eur J Cancer 1999;35:973-7. Faivre J, Tazi MA, El Mrini T, et al. Faecal occult blood screening and reduction of colorectal cancer mortality: a case-control study. Br J Cancer 1999;79:680-3.

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Elmunzer et al Scheitel SM, Ahlquist DA, Wollan PC, et al. Colorectal cancer screening: a community case-control study of proctosigmoidoscopy, barium enema radiography, and fecal occult blood test efficacy. Mayo Clin Proc 1999;74:1207-13. Hoff G, Grotmol T, Skovlund E, et al. Risk of colorectal cancer seven years after flexible sigmoidoscopy screening: randomised controlled trial. BMJ 2009;338:b1846. Atkin WS, Edwards R, Kralj-Hans I, et al. Once-only flexible sigmoidoscopy screening in prevention of colorectal cancer: a multicentre randomised controlled trial. Lancet 2010;375:1624-33. Segnan N, Armaroli P, Bonelli L, et al. Once-only sigmoidoscopy in colorectal cancer screening: follow-up findings of the Italian Randomized Controlled TrialdSCORE. J Natl Cancer Inst 2011;103:1310-22. Schoen RE, Pinsky PF, Weissfeld JL, et al. Colorectal-cancer incidence and mortality with screening flexible sigmoidoscopy. N Engl J Med 2012; 366:2345-57. Thiis-Evensen E, Hoff GS, Sauar J, et al. Population-based surveillance by colonoscopy: effect on the incidence of colorectal cancer. Telemark Polyp Study I. Scand J Gastroenterol 1999;34:414-20. Kahi CJ, Imperiale TF, Juliar BE, et al. Effect of screening colonoscopy on colorectal cancer incidence and mortality. Clin Gastroenterol Hepatol 2009;7:770-5; quiz 11. Singh H, Nugent Z, Demers AA, et al. The reduction in colorectal cancer mortality after colonoscopy varies by site of the cancer. Gastroenterology 2010;139:1128-37. Jacob BJ, Moineddin R, Sutradhar R, et al. Effect of colonoscopy on colorectal cancer incidence and mortality: an instrumental variable analysis. Gastrointest Endosc 2012;76:355-64.e1. Manser CN, Bachmann LM, Brunner J, et al. Colonoscopy screening markedly reduces the occurrence of colon carcinomas and carcinoma-related death: a closed cohort study. Gastrointest Endosc 2012;76:110-7. Zauber AG, Winawer SJ, O'Brien MJ, et al. Colonoscopic polypectomy and long-term prevention of colorectal-cancer deaths. N Engl J Med 2012; 366:687-96. Baxter NN, Goldwasser MA, Paszat LF, et al. Association of colonoscopy and death from colorectal cancer. Ann Intern Med 2009;150:1-8. Baxter NN, Warren JL, Barrett MJ, et al. Association between colonoscopy and colorectal cancer mortality in a US cohort according to site of cancer and colonoscopist specialty. J Clin Oncol 2012;30:2664-9. Muller AD, Sonnenberg A. Protection by endoscopy against death from colorectal cancer: a case-control study among veterans. Arch Intern Med 1995;155:1741-8. Shaukat A, Mongin SJ, Geisser MS, et al. Long-term mortality after screening for colorectal cancer. N Engl J Med 2013;369:1106-14.

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