Report in English with a Dutch summary (KCE reports 45A)

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86 Screening for Colorectal Cancer KCE reports vol.45 5.5.5 Colonoscopy In some countries there is considerable interest in using colonoscopy as a screening tool. Potential advantages are clear. It is highly accurate for the detection of CRC with a sensitivity reported to be as high as 99,0% (95% CI: 97,1% to 99,9%) and a specificity of virtually 100% 329. It has to be appreciated that sensitivity is not 100% as has been demonstrated by back-to-back colonoscopy studies, which show that adenomas and occasionally carcinomas can be overlooked by even experienced colonoscopists 290. In addition, a study comparing state-of-the art CT-colography with colonoscopy suggests that the sensitivity of colonoscopy for adenomatous polyps may be as low as 87,5% 320. There have been no published RCTs on the efficacy of colonoscopy as a screening strategy for colorectal cancer 181, 219. All data regarding efficacy and risk came from studies of its use as a diagnostic or therapeutic tool limiting the direct relevance of the evidence to the screening context 275, 194. Conclusions must therefore necessarily be limited. It is clear, however, that colonoscopy has high sensitivity and specificity but also that the risks of physical harm from colonoscopy are higher than from either FOBT or FS. Those are also dependent upon the operators experience, as discussed before. The most important study in the literature in terms of estimating the efficacy of screening colonoscopy is a case-control study conducted among U.S. military veterans 385. The study group consisted of 4.411 veterans deceased of colorectal cancer between 1989 and 1992. The control group was derived from living control patients and dead control patients without colorectal cancer matched by age, sex, and race to each case. Using this study design it was found that colonoscopy reduced death rates from colorectal cancer with an odds ratio of 0,41 (range 0,33 - 0,50) In addition, comparison with the living control group revealed that the protective effects lasted for five years and that polypectomy was particularly protective. Similar results were found when the dead control group was studied. Again it should be emphasized that this study was observational and its design far from perfect, particularly as the indications for colonoscopy in the study group were varied and included investigation of symptomatic patients. There are, of course, abundant uncontrolled data on screening colonoscopy and perhaps the most useful study was carried out in 13 Veterans Affairs (VA) medical centers to determine the utility of colonoscopy in detecting colorectal neoplasia in asymptomatic individuals aged 50 to 75 283. Of 17,732 patients screened for participation, 3.196 were enrolled; 3.121 of the enrolled patients (97,7%) underwent complete examination of the colon. The mean age was 62,9 years and 97% were males. An adenoma of at least 10 mm diameter was detected in 7,9% and invasive cancer in 1%. Of 1.765 subjects with no adenomas distal to the splenic flexure 48% had proximal adenomas or cancers. It can be concluded from this study that if colonoscopy were used as a screening tool in men aged between 50 and 75 the participation rate would only be 20% and only 1% of colonoscopies would detect colorectal cancer. Thus, although colonoscopy is widely used to screen asymptomatic individuals on demand (targeted screening), it seems very unlikely that it could ever be used as an effective population screening modality. 5.5.6 Double contrast barium enema (DCBE) There have been no published RCTs on the efficacy of DCBE as a screening strategy for colorectal cancer 275, 181, 219. In the National Polyp Study the performance characteristics of DCBE were compared to those of colonoscopy
KCE reports vol.45 Screening for Colorectal Cancer 87 by examining those who had undergone a prior colonoscopic polypectomy345. In this study the DCBE was less sensitive in detecting adenomas than colonoscopy and the sensitivity was associated with the size of the adenomas. This finding was confirmed by other studies194, 386. Johnson et al. 386 compared relative sensitivity and specificity of CT colonography with DCBE for the detection of colorectal polyps in a population reflective of a screening setting. In addition the potentially added value of double reading at CT colonography was assessed, using endoscopy as the gold standard . This prospective, blinded study comprised 837 asymptomatic persons at higher than average risk for colorectal cancer who underwent CT colonography followed by same-day DCBE. Examinations with polyps 5 mm in diameter were referred to colonoscopy. CT colonography readers detected 56% - 79% of polyps 10 mm in diameter. In comparison, the sensitivity with DCBE varied between 39% and 56% for the 31 polyps 10 mm. All of the readers detected more polyps at CT colonography than DCBE, but the difference was statistically significant for only a single reader (p = 0,02). Relative specificity for polyps 10 mm on a per-patient basis ranged from 96% to 99% at CT colonography, and 99%-100% at DCBE. Double-read CT colonography detected significantly more polyps than DCBE (81% vs. 45% for polyps 1 cm (p 0,01), and 72% vs. 44% for polyps 5 - 9 mm (p 0,01)). The authors concluded that double-read CT colonography is significantly more sensitive in detecting polyps than single-read DCBE. 5.5.7 Virtual colonoscopy Virtual colonoscopy is a rapidly evolving technology under evaluation as a new method of screening for colorectal cancer. However, up to today there have been no published RCTs on the efficacy of virtual colonoscopy as a screening strategy for CRC and its performance in this field has not yet been studied in typical screening populations387, 328, 219. The Blue Cross and Blue Shield Technology Evaluation Center report, Volume 10, nr. 6 387 rightfully underlines that there are many possible methods used in the literature to analyze the diagnostic performance of CT colonography. The 2 most common methods are referred to as a per-polyp analysis and a per-patient analysis. In the per-polyp analysis, the capability of CT to detect all polyps is calculated in terms of sensitivity relative to a reference standard. Specificity cannot be calculated because there is no real denominator for the absence of a polyp. Although a per-polyp analysis gives some insight regarding the technical capability of CT, it is not as relevant as a per-patient analysis in determining its clinical utility. Furthermore, in most studies, the per-polyp analysis gives a misleading estimate of sensitivity as it would be used clinically. The studies usually consider CT colonography to have matched a polyp seen on colonoscopy if the size of the polyp seen on CT is within 50% of the size determined on colonoscopy. For example, a polyp measured as 5 mm on CT is considered a positive finding for a polyp measured as 10 mm on colonoscopy. However, this should not be considered as a positive finding in a per-patient analysis, because to allow a 5 mm size threshold to be a positive test for detecting 10 mm polyps would require such a threshold to be also applied to the assessment of specificity. Thus, all patients who are accurately identified as having only 5 mm polyps with CT colonography should be counted as false positive if one requires a 5 mm threshold to identify a 10 mm polyp. Although CT colonography is considered to be more sensitive for large polyps, clinically this greater sensitivity may not bear out because the interpretation must not only identify a large polyp, but also correctly classify it as a large polyp. Thus,
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KCE reports 1. Effectiviteit en kos
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