Comparing apples to applesReferring to Pedersen L et al. p. 733–741
25 July 2019 (online)
In the current issue of Endoscopy, Pedersen et al.  present data on the risk of post-colonoscopy colorectal cancer (PCCRC) in Denmark and we congratulate the authors for their interesting and very valuable study. They used near-perfect Danish registries to obtain very meaningful data. These registries included The Danish Cancer Registry, which contains coded information about every Danish cancer patient with histology and TNM classification, the Danish National Patient Registry, and the Danish National Prescription Registry, which contains information about every contact with the public health care service including dates, diagnoses, treatments, and procedures.
The availability of such high quality tools enabled Pedersen et al. to calculate the rate of PCCRC over a large time span and, most importantly, using three different methods of calculation. The authors were able to adjust their methodology to the methods used by other groups in order to compare national data. For comparison with Sweden, they used methodology described by Forsberg et al.  and found that rates of PCCRC are higher in Denmark than in Sweden. Similarly, by using English methodology, they were able to compare their data with those from the study by Morris et al. , with a similar conclusion – the Danish PCCRC rate was significantly higher than the most recent calculations from the UK. These findings have led to an obvious conclusion that there is a need to speak loudly about PCCRCs and analyze reasons for insufficient colonoscopy performance in Denmark. Interestingly, the authors speculated about various reasons including a lack of proper training for Danish endoscopists and also the fact that colonoscopy in Denmark is performed mainly by surgeons. The quality of endoscopy training during residency in surgery is considered inferior to that offered during a gastroenterology specialty.
“...standardized training/curricula are necessary for EU endoscopists to avoid inappropriate quality of endoscopy.”
The third method Pedersen et al. used to calculate PCCRC rate followed the World Endoscopy Organization guidance . In these guidelines, the sum of PCCRCs is divided by the sum of PCCRCs and clinically diagnosed cancers to obtain the rate. These calculations have shown that, despite poorer Danish results compared with Sweden and the UK, the overall trend was positive, meaning a significant drop in the rate of 3-year PCCRC between 2001 and 2012, from 22.5 % to 7.9 %.
In the second part of their study, Pedersen at al. aimed to identify risk factors associated with PCCRC. Regrettably, the data to calculate the key performance measures for colonoscopy (such as rate of adequate bowel preparation, cecal intubation rate or adenoma detection rate) were not available. As the quality of colonoscopy is considered to be a main contributor to the risk of PCCRC , the multivariable analysis performed within the study in search for associated risk factors may be misleading. In particular, we are concerned about the finding that indicated a previous diagnosis of diverticulitis as an important risk factor for PCCRC. This could easily lead to a conclusion that diverticulitis is a causal factor of CRC according to a common sense rule that inflammation may lead to cancer. We warn against drawing this conclusion, especially in light of a recent paper, also from Denmark and using the same medical registries, which has proven that although CRC is associated with diverticulitis, in the majority of cases this applies only within 500 days of the diverticulitis episode . Two other large studies published within the past 8 years have also documented that diverticular disease is associated with diagnosis of CRC but only within 1.5 years from the onset of diverticular disease . This is most probably caused by the similarity of symptoms between the diseases leading to misdiagnosis. Nevertheless, it must be remembered that current guidelines recommend performing a colonoscopy within 1 year after healing of diverticulitis. If colonoscopy had been performed routinely in Denmark during the study period, then most probably the association between previous diverticulitis diagnosis and PCCRC, as described by Pedersen et al., would not have been detected.
It would be worth conducting similar studies to compare colonoscopy performance across all European countries, although a lack of high quality medical registries similar to the ones in Denmark might make this impossible for some European Union (EU) member states. Alternatively, we would like to draw Endoscopy readers’ attention to an interesting, recently published paper reporting a novel method of calculating the quality of an overall medical care system in relation to CRC . Data were collected on all CRCs diagnosed and treated at a single medical institution in Houston, Texas, between 2007 and 2016. The authors identified 572 cancers after excluding those related to familial polyposis syndrome, Lynch syndrome, and inflammatory bowel disease. Of those, 197 (34.4 %) were screen detected and 375 (65.6 %) were not screen detected. Of the latter CRCs, 84 (14.7 %) were never screened and as many as 291 (50.9 %) were previously screened but the screening did not result in a diagnosis of cancer. Interestingly, the majority (72.9 %) of CRCs occurred after fecal immunochemical testing (FIT) and in two-thirds of this group patients were supposedly “guilty” (e. g. did not return their FIT samples) and in one-third providers were “guilty” of not diagnosing cancer despite availability of FIT screening (e. g. providers did not provide follow-up). There were also 79 patients with PCCRC, where 35 were classified as interval cancer and 44 were non-interval CRCs (75 % patients and 25 % providers were classified as responsible for the failure to detect cancer). The authors claimed that classification of cancers diagnosed and treated at a given medical institution into these three categories – screen detected, nonadherence CRC (i. e. those not detected due to patient or provider failure), and interval CRC – and reporting the proportions between these three classes would be another and novel quality indicator of system organization within a defined medical catchment. Temporal trends could also be established.
The study by Pedersen et al. clearly shows that with the availability of appropriate tools, it is possible to compare “apples to apples” and draw meaningful conclusions. It should also be emphasized that standardized training/curricula are necessary for EU endoscopists to avoid inappropriate quality of endoscopy. Fortunately, the European Society of Gastrointestinal Endoscopy is working on this improvement.
- 1 Pedersen L, Valori R, Bernstein I. et al. Risk of post-colonoscopy colorectal cancer in Denmark: time trends and comparison with Sweden and the English National Health Service. Endoscopy 2019; 51: 733-741
- 2 Forsberg A, Hammar U, Ekbom A. et al. Post-colonoscopy colorectal cancers in Sweden. Eur J Gastroenterol Hepatol 2017; 29: 855-860
- 3 Morris EJA, Rutter MD, Finan PJ. et al. Post-colonoscopy colorectal cancer (PCCRC) rates vary considerably depending on the method used to calculate them: a retrospective observational population-based study of PCCRC in the English National Health Service. Gut 2015; 64: 1248-1256
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