Gastroenterology
Volume 126, Issue 5 , Pages 1474-1477, May 2004

Quality control for flexible sigmoidoscopy: which polyps count?

  • Ann G Zauber

      Affiliations

    • Corresponding Author InformationAddress requests for reprints to: Ann G. Zauber, Ph.D., Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, Box 44, New York, New York 10021 USA; fax: (646) 735-0012
    • Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, New York, USA

Article Outline

 

Screening1, 2, 3, 4 can prevent colorectal cancer, the second leading cause of cancer deaths in the United States, by detecting cancer at an early stage and by removing adenomatous polyps.5, 6 Screening is now recommended for asymptomatic, average-risk individuals age 50 years or older in the US.1, 7, 8, 9 Flexible sigmoidoscopy is 1 of the 4 recommended screening tests. Atkin et al.,10 based on their study reported in this issue of Gastroenterology, conclude that a high-quality flexible sigmoidoscopy program will find one or more adenomas in 15% of patients examined. They hypothesize that this level of positive results will translate to reduced incidence and mortality from colorectal cancer.

The primary aim of the report from the United Kingdom Flexible Sigmoidoscopy Screening Trial, which randomized participants from the general population to a once-in-a-lifetime screening flexible sigmoidoscopy or to usual care, was to assess whether screening flexible sigmoidoscopy reduces colorectal cancer incidence by 40% over 10 years and colorectal cancer mortality by 40% over 15 years.11 An interim analysis on the incidence and mortality reduction is expected in 2004. In this trial, the flexible sigmoidoscopy screening examination is offered to a more restricted age group (ages 55–64) than in the United States (where it is recommended to begin at age 50 and to be repeated every 5 years)1, 7, 8, 9 and is used as a triage examination to decide which participants will never have another colorectal cancer screening examination (“once-in-a-lifetime” examination) and those who will need further follow-up. High-quality examinations are always of importance but even more so if a single flexible sigmoidoscopy examination is used to determine a person’s access to continuing screening.

Quality assurance assessment was designed into the structure of the UK Flexible Sigmoidoscopy Screening Trial.12 Each of the 13 centers had identical endoscopy equipment and followed standardized protocols for conducting the examinations. Training and evaluations of endoscopists were also standardized. Nevertheless, there was wide variation in the rates of adenoma detection from center to center. The adenoma detection rate for the center with the highest rate (15.9%) was almost double that of the center with the lowest detection rate (8.6%). There continued to be variability among the centers even when differences were taken into account regarding participant characteristics of age, gender, family history, and smoking; center characteristics of the geographic area’s colorectal cancer incidence rates; and the endoscopist’s medical specialty or previous experience. The authors believe that the lower detection rates occur when endoscopists miss a sizeable proportion of adenomas, particularly small adenomas, and conclude that the adenoma detection rate achieved by the endoscopists with the highest rates should be achievable by all endoscopists.

The conclusion that all endoscopists should achieve an adenoma detection rate of 15% for screening flexible sigmoidoscopy in those aged 55 or older warrants discussion on several points: (1) whether detection of adenomas of all sizes is the appropriate surrogate measure for quality of examination, (2) whether the level of 15% is appropriate for all populations, (3) whether training programs can ensure attaining this rate of detection, and (4) how to implement measuring adenoma rates per endoscopist in general clinical practice. Perhaps the most important question is whether higher adenoma detection rates will translate to a higher reduction in colorectal cancer incidence and mortality compared with lower detection rates. If so, then the overall adenoma detection rates would be an appropriate surrogate for future benefit in reducing colorectal cancer incidence and mortality.

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Should detection of all adenomas be the surrogate marker for quality of examination? 

The authors chose detection of all adenomas as the standard of performance. However, in a screening population with flexible sigmoidoscopy, as was shown here, most of the adenomas detected are small (12.1% had 1 or more adenomas but only 3.3% had 1 or more large [>1 cm] polyps). Consequently, the measure for all adenomas is mainly based on detecting small adenomas. A rationale for using a standard based on finding small adenomas could be the hypothesis that small adenomas are themselves dangerous in terms of long-term prognosis and therefore must be removed. Unfortunately, there are little direct data about growth rates of small adenomas left intact until a subsequent examination.13 Not all can be clinically important because small adenomas are so common, but there is at least potential for malignancy that can rapidly grow to incurability in a small percentage of the small adenomas.14 There have been differences of opinion as to the importance of the small adenoma in the distal colon and rectum as an indicator for further neoplasia.15, 16, 17, 18, 19, 20 A second rationale is that detection of all adenomas has been suggested as a quality-improvement target for colonoscopy under the assumption that adequate technique to detect small adenomas should also detect larger adenomas.21 However, Atkin et al.10 showed that the detection rate for small polyps was not correlated with the detection of large polyps. Instead, the adenoma detection rates were correlated with detection rates of nonadenomatous polyps. Hixson et al.22 and Rex et al.23 have shown that larger polyps are infrequently missed on endoscopy but that 20% or more of small polyps are missed. A third rationale is that detection of all adenomas increases the chance of detecting multiple adenomas. Multiple adenomas of any size (particularly 3 or more adenomas) are an important predictor of advanced adenomas at surveillance colonoscopy.24 It is the advanced adenoma—defined on the basis of larger size (≥1 cm), villous component, or high-grade dysplasia—that appears to have the highest malignant potential and serves as the bridge between benign and malignant neoplasia. Consequently, at a minimum, detection and removal of the advanced adenoma should be the primary target for a screening program.25 Whether detection and removal of all adenomas (including small) by flexible sigmoidoscopy is a meaningful measure by which to evaluate endoscopists’ performance will depend on whether this study subsequently shows that colorectal cancer incidence or mortality differ by endoscopist detection rates.

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Can the 15% detection rate for adenomas by flexible sigmoidoscopy be generalized to other screening populations? 

The average detection rate of adenomas in the study by Atkin et al.10 (12%) was high, exceeding all but 3 of 20 studies reviewed in the author’s Table 4, and higher than the 10% rate used in planning this study. But the detection rate chosen to be acceptable (15%) was even higher than the overall rate because it was based on the average for the highest centers. The determination of which centers were to be included as high detectors was based on statistical analyses of the variability, but, at this point in time, we do not know whether these statistical differences translate to important clinical differences in the outcomes of cancer incidence or mortality.

Several factors could affect the absolute level of adenoma findings in other settings and the “generalizeability” of these results. The authors noted marked differences in the adenoma detection rate for men and for women and suggested different levels of detection by gender. Age was related only modestly to level of adenomas detected, but the age range of the trial was restricted to 55–64 years old. However, in the United States, screening is advocated for younger persons—average-risk persons beginning at age 50—and for those 65 and older. Prevalence might vary widely, because of age, in these groups. There are also other risk factors for adenomas to consider such as obesity, lack of physical activity, smoking, family history, nonsteroidal anti- inflammatory drugs such as aspirin and cyclooxygenase-2 inhibitors, calcium supplementation, multivitamin vitamins (with folate), and hormone-replacement therapy.26, 27, 28, 29, 30, 31, 32, 33, 34 Although not a factor in the current trial, in the United States, the level of previous screening would also be important to measure because those with a previous negative screening examination would be less likely to have adenomas detected.35 Furthermore, the endoscopists in the study by Atkin et al.10 who were physicians in training, knew that their performance was being monitored and feedback would be provided. Additional adjustments for differing patient populations would be needed were these recommendations to be put into clinical practice for quality assurance in the United States.

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Can training ensure a high detection rate of adenomas? 

Health providers performing flexible sigmoidoscopy in a screening program should have proficiency in performing this examination.1 This study documents the need for standardized training for flexible sigmoidoscopy if detection of all adenomas should be used as the measure of endoscopist performance. The authors show that there is a marked learning curve for endoscopic detection of adenomas, which requires more than 400 examinations before reaching proficiency. In addition, the authors state that the endoscopists who had the lowest rates for the study could be identified by 600 examinations and suggest that such endoscopists might require further remedial help. The authors plan to report in a separate publication what procedural factors were related to higher adenoma detection rates. The procedural factors might include measures of time required to complete the flexible sigmoidoscopy, documenting the reach of the flexible sigmoidoscope, assuring good bowel preparation, repeating procedures when segments are poorly visualized, ensuring follow-up of positive findings, or other factors associated with the examination. Such findings will be crucial to link what techniques and quality-assurance standards must be stressed to achieve an acceptable detection rate.

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How could monitoring of adenoma detection rates be implemented in clinical practice in the united states? 

Health care systems should establish standards and operating procedures to ensure high-quality screening examinations.1 In the United Kingdom, colorectal cancer screening is primarily organized through structured government programs, whereas colorectal cancer screening in the United States is not centrally organized. There is a challenge in the United States to assess who is performing the procedures, to monitor and report the adenoma detection rate per endoscopist, to ensure adequate numbers of examinations to provide evaluation, and to evaluate the screening characteristics of the participants. Primary care physicians perform 65% of all sigmoidoscopy procedures in the United States (average of 7 procedures a month), gastroenterologists perform 25% of the flexible sigmoidoscopies (average of 14 procedures a month), and general surgeons perform 10% (average of 7 per month).36 In addition, only 39% of primary care physicians who perform sigmoidoscopy also perform a biopsy for any polyps detected. Consequently, the sigmoidoscopy practice patterns that might be recommended based on the United Kingdom flexible sigmoidoscopy study could be difficult to implement or to monitor in a dispersed medical provider group. These problems led Brown et al.,36 Levin and Palitz,37 and Atkin et al.12 to suggest possible establishment of dedicated and coordinated screening centers for colorectal cancer.

In summary, the study by Atkin et al.10 is informative about considering quality-assurance issues for flexible sigmoidoscopy screening. However, it is not yet clear that the proposed approach will translate to an impact on the primary outcomes of cancer incidence and cancer mortality. In the United States, major logistic problems would need to be addressed to implement the kind of approach now being used in the United Kingdom. The incidence and mortality results that will be reported in the next few years will provide an important test of the hypothesis that the sites with a higher adenoma detection rates had a higher reduction in incidence and mortality. The current results present a worthwhile challenge and should stimulate us to think about quality assessment measures of colorectal cancer screening programs in the United States.

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PII: S0016-5085(04)00482-2

doi:10.1053/j.gastro.2004.03.029

Gastroenterology
Volume 126, Issue 5 , Pages 1474-1477, May 2004