Achieving the potential of colonoscopy screening

There is now strong evidence that lower bowel endoscopy can prevent colorectal cancer (CRC) and good evidence that the strength of this effect depends on the quality of the procedure [1] [2] [3]. Two studies have demonstrated that adenoma detection rate (ADR) predicts interval cancer [2] [3]. One of these studies demonstrated a reduction in death from CRC in patients screened by colonoscopists who were high adenoma detectors compared with patients screened by low detectors [3]. High quality colonoscopy is critical to the effectiveness of CRC screening.

A study by Waldmann et al. in the current issue of Endoscopy [4] focuses on ADR as the key quality marker of colonoscopy in the context of nonprogram-based CRC screening. The key finding was that ADR improves over time. The authors linked this change to a technique referred to in the improvement science literature as “audit and feedback” [5]. The detection of proximal lesions improved more than adenoma detection but detection of advanced adenomas (AADR) decreased over time [4].

The results and interpretation have to be viewed with caution because this was not a controlled study and there were limitations of the methodology, especially in relation to data acquisition. Colonoscopists were requested to submit an electronic data form in addition to preparing a colonoscopy report, but not all screening cases were submitted. Validation of data quality showed submitted reports to be accurate, but it is not known whether colonoscopists might have, without deliberate intent, “selected” cases for submission.

There are two key aspects to consider in relation to this study. First, what do the changes in performance actually mean for patients? Second, is there anything we can learn from the study that can be applied to improve quality in other contexts?

Ultimately, screening colonoscopy is intended to improve outcomes of CRC, namely to reduce death and incidence. CRC mortality is a critical outcome measure, but not a useful performance measure of colonoscopy as there are too many other factors that can affect mortality. Incidence, on the other hand is not affected by other health care interventions. The problem with incidence is that timelines are too long for monitoring day-to-day performance. Postcolonoscopy CRC is a good marker of colonoscopy quality but complex data linkages are required to provide a reliable measure [6]. Importantly, the measure is usually only available years after the event. Finally, the sample size required for an accurate estimate of performance precludes the use of postcolonoscopy CRC or interval cancer as a measure for individual performance.

We are left therefore with surrogates of the things that really matter to patients: ADR and withdrawal time, which is itself a surrogate of a surrogate. The study by Corley et al. [3] would indicate that the 6 % improvement in ADR over the time period of the study would lead to an additional 18 % reduction in CRC, if American data can be applied in a European context. Such a reduction would be meaningful to patients. This study considered two other surrogates: proximal lesions and AADRs.

There is increasing interest in the role played by proximal lesions, many of which are sessile serrated lesions (SSLs) [7]. It is thought that SSLs can be a forerunner of an accelerated pathway to cancer. The observation of high rates of interval or postcolonoscopy CRC on the right side of the colon [8] supports the idea of an accelerated pathway. It has been proposed that fast-growing tumors appear after a negative colonoscopy [9]. However, it seems equally likely that higher rates of right-sided postcolonoscopy cancer could be due to incomplete colonoscopies and poor bowel cleansing (which is usually a bigger problem in the right colon) leading to a higher risk of missing right-sided SSLs. The jury is out on whether right-sided or SSLs lead to more rapid development of cancer, or whether they are a superior marker of quality.

The idea that AADR is a key marker of quality has been around much longer than that for proximal lesions. Surveillance guidelines are based on the prognostic potential of advanced lesions [10] so why wouldn’t AADR be a better marker of quality? Intuitively, it makes sense: larger and more dysplastic lesions are more likely to lead to cancer, therefore high AADR will be associated with lower subsequent incidence of cancer. There are several problems with this. Most high-volume colonoscopists will have excised sub 10 mm lesions that contain malignancy – it is difficult therefore to ignore the small lesions. Also, we know there is variation in the definition of advanced lesions because of variation in measurement of polyp size [11] and variation in reporting of pathology, particularly that of dysplasia [12].

The more complicated the data acquisition and the more variation in reporting, the more unreliable the measure becomes. Clinicians lose confidence in a measure if they do not think it is being reliably reported, and once confidence is lost, they ignore the data. Thus, until we have more certainty about these alternative performance indicators it is probably appropriate for endoscopy services to keep it simple and measure ADR or, at the very least, polyp detection rates, until the evidence base improves.

The changes in the three indicators over time in the study by Waldmann et al. [4] – ADR rising steadily over time, a large increase in proximal lesions, and a steady fall in AADR – mirror the relative awareness of these indicators over time. In recent years, there has been a continuing focus on ADR, increasing attention on proximal lesions, and declining interest in advanced lesions as a potential marker of quality. Procedural factors may also be important; for example, improved bowel preparation observed in the Waldmann study [4] will have facilitated detection of proximal lesions.

In the absence of compelling data, endoscopists should aim to assiduously clear the colon of all polyps except the obvious and insignificant ( < 5 mm) distal hyperplastic polyps. It is clear from the literature that some individuals are able to do this consistently. There is no reason why everyone cannot do so and if everyone did, we would see major improvements in CRC incidence and mortality.

Having reliable feedback of performance is one critical requirement in the process of improving ADR, but it is not the only one. An individual’s belief that it will make a difference, being motivated to change, and working in an environment that is conducive to high quality (time, staff, equipment, and excellent bowel preparation) are all critically important. Only then can an individual apply the necessary knowledge and good technique to achieve excellent outcomes.

Endoscopy services, whether they do screening colonoscopy or not, should have systems in place to monitor ADR and, critically, to feed back the results on a regular basis. There should be provision to motivate and support those colonoscopists who need to improve their detection rates and, importantly, to stop those who refuse to improve, or are unable to do so, from performing colonoscopy.

• References

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