Abdominal Imaging

ª Springer Science+Business Media, Inc. 2005 Published online: 5 December 2005

Abdom Imaging (2006) 31:297–301 DOI: 10.1007/s00261-005-0368-7

PERSPECTIVE

CT colonography: screening in individuals at high risk for colorectal cancer T. M. Gallo,1 G. Galatola,2 C. Laudi,2 D. Regge1 1

Radiology Unit, Institute for Cancer Research and Treatment, Strada Provinciale 142 Km 3.95, 10026 Candiolo (Turin), Italy Gastroenterology Unit, Institute for Cancer Research and Treatment, Strada Provinciale 142 Km 3.75, 10026 Candiolo (Turin), Italy 2

Abstract The use of computed tomographic colonography (CTC) as a screening test for colorectal cancer is being advocated with growing enthusiasm by physicians and the public as stronger evidence of its validity and limited invasiveness emerges from the literature. Because the approach to surveillance of colorectal cancer depends on an individual’s degree of risk category, which depends on familial and personal histories, it seems logical that the diagnostic performance and cost efficacy of screening CTC may differ according to the characteristics of the target population. Although CTC seems a valid option in low- to average-risk populations, pending a careful assessment of its cost and estimates of its cost efficacy, there are some important issues that should be addressed when it comes to considering its use in high-risk patients. The expected larger number of induced colonoscopies and higher false-positive rates are likely to have a great influence on CTC costs, but if its implementation causes a dramatic increase in the number of patients willing to undergo screening, thanks to its acceptability, then the cost efficacy ratio may ultimately become competitive with all other screening strategies for colorectal cancer. We strongly feel that large and well-conducted trials are needed to clarify the role of CTC in screening patients at increased risk of developing colorectal cancer. Key words: Computed tomographic colonography —Conventionalcolonoscopy—Colorectal cancer—Screening

Colorectal cancer (CRC) represents the second most common cause of cancer mortality in Western countries. In Europe, about 340,000 new cases are recorded and Correspondence to: T. M. Gallo; email: [email protected]

190,000 patients die from the disease every year [1]. Despite advances in the treatment of this disease, the 5-year survival rate is only 62% [2]. It has been well established that survival improves when diagnosis is made at an earlier stage, thus providing a rationale for population screening [3]. Screening tests for CRC have been shown to be cost effective in decreasing specific mortality [4]. The cumulative lifetime risk of developing CRC in the general population of Western countries is estimated at about 6% [2], whereas the relative risk for the individual patient varies according to personal and family histories; as a consequence, screening strategies, in terms of which test and the timing of when it should be repeated differ and all recent major guidelines published have stratified patients to be screened into various risk categories [3]. The average-risk individuals are those who are 50 years or older with no personal or family history of colorectal adenoma or CRC. In the high-risk category are those patients who have a family or personal history of colorectal adenocarcinoma or adenoma. A family history is generally defined as a diagnosis of CRC or adenomas in any first-degree relative at an age younger than 60 years or in at least two first-degree relatives at any age excluding the well-known criteria for hereditary CRC syndromes such as familial adenomatous polyposis or hereditary nonpolyposis colon cancer [5], whose discussion is outside the scope of this review. The number of potential at-risk relatives is sizeable, considering that approximately 10% to 20% of patients with CRC have at least one first-degree relative who is affected by the same disease [6, 7]. In asymptomatic at-risk relatives, the relative risk is increased two- to fourfold compared with the general population, and the risk progressively increases with the decreasing age of the index case in the family. Personal history is defined as a history of polypectomy of ‘‘advanced’’ adenomas or resection of CRC with curative intent. After polypectomy, metachronous ade-

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nomas have been reported in 20% to 50% of patients [8– 12]. In the National Polyp Study, the reported 3-year incidence of metachronous adenomas ranged from 32% to 42%, whereas the incidence for advanced lesions was only 3%. A two- to fourfold increased risk of CRC has been observed in patients whose index adenoma was advanced, and the risk was five- to sixfold higher in those with multiple adenomas in comparison with the general population [13, 14]. Postpolypectomy surveillance for identification and removal of metachronous adenomas is mandatory, but it should be tailored to the characteristics of the adenomas removed at the time of index conventional colonoscopy (CC) [15–17]. Patients with longstanding chronic inflammatory bowel disease involving the colon are also included in the high-risk category. Surveillance is advised for ulcerative colitis and Crohn colitis because the cancer risk is similar in both diseases and surveillance programs increase survival [18] by carrying out CC and serial biopsies every 1 to 2 years after 8 years in cases of pancolitis or 15 years in left-side colitis. Biopsy specimens should be taken every 10 cm and on any strictures, mass lesions, polyps, and adjacent flat mucosa to detect dysplasia. Dysplasia frequently appears on flat areas of the mucosa, making it careful endoscopic visualization of the whole mucosa essential because its appearance is a strong indication for colectomy.

Screening methods The approach to high-risk patients is not firmly established. Whether they should be monitored in the same way as those at average risk or be screened more vigorously remains to be definitively determined. Colonoscopy remains the procedure of choice to screen members of families with hereditary colon cancer syndromes (familial adenomatous polyposis and hereditary nonpolyposis colon cancer) [19] and may be cost effective in first-degree relatives of patients who developed CRC or advanced adenomas before the age of 60 years. For these patients CC is suggested every 5 years starting at the age of 40 years or 10 years younger than the earlier case in the family, whichever comes first, until 65 years of age [3]. For patients with a history of polypectomy, colonoscopic surveillance is advised at 3- to 5-year intervals according to widely implemented guidelines (American College of Gastroenterology guidelines for colorectal adenomas: http://www.east.elsevier.com/ajg/ issues/9511/ajg3434fla.htm). Despite CC being the optimal screening test in this setting, it is still a poorly accepted test because it requires bowel preparation and conscious sedation and carries a number of risks, including perforation with a rate up to one per 1000 [20]. This justifies the effort of searching for a less invasive, more rapid, and well-tolerated screening method, which would meet better acceptance.

Computed tomographic colonography Computed tomographic colonography (CTC) is a minimally invasive procedure that allows the air-to-mucosa interface of the large bowel wall to be visualized using abdominal CT after inflation with air of the colon previously emptied by standard cleansing procedures. Viewing of the colon mucosal surface is obtained by sequential visualization of two-dimensional axial images or by dedicated software that allows the radiologist to virtually ‘‘travel’’ through the center of the colon simulating what is seen on CC [21, 22]. CTC may have several advantages over traditional CC: provided the colon preparation is optimal, the entire colon can always be visualized; there is no need for sedation; patient acceptance is better; the patient spends just 10 to 15 min completing the test, although an additional 15 to 30 min is needed for reporting; and it is less operator dependent and more standardized to the point that automated diagnosis may become an option in the future [23–25]. Thus, CTC has been perceived by radiologists and patients as a new and exciting development for diagnosing colorectal diseases and particularly as a potential breakthrough for screening purposes [26, 27]. Studies on the diagnostic performance of CTC were carried out first in symptomatic patients who had a high prevalence of clinically significant colorectal lesions; compared with traditional CC, which remains the gold standard, CTC has a sensitivity of approximately 90% for lesions of at least 10 mm, which decreases to 50% or less for lesions smaller than 6 mm [28–31]. After such encouraging results, radiologists have focused their attention on assessing the diagnostic values of CTC in asymptomatic patients by trying to simulate screening conditions in which the prevalence of clinically significant lesions is lower and whose characteristics are likely to differ from those of symptomatic patients [32]. Three major studies enrolled average-risk asymptomatic patients but reported diagnostic values that were not consistent with each other, thus leaving unanswered the question of whether CTC can currently be used as a screening test for CRC in the general population [33–35]. High-risk patients generally have been included in studies involving symptomatic patients [29, 36]; in the few cases in which results have been presented separately [37, 38], the diagnostic values of CTC did not seem to differ, although such a conclusion cannot be supported by a sufficient sample because this comparison was not a primary aim of any of these studies. The issue of separating symptomatic from asymptomatic patients and average-risk from high-risk asymptomatic patients is relevant. Although the difference in the expected prevalence of clinically significant lesions is not likely to affect the estimate of the diagnostic values of CTC, the neoplastic lesions that characterize

T. M. Gallo et al.: Screening patients at high risk for colorectal cancer

these different groups of people may differ, thus explaining the wide variability of results that have been reported. In symptomatic patients, the great majority of lesions is likely to be sizeable and frankly polypoid; in asymptomatic patients, most lesions are likely to be more subtle and the prevalence of flat adenomas, which remains beyond the diagnostic possibility of CTC, may differ between high- and average-risk patients. [39]. Even CC may fail to detect such lesions, and techniques of chromoendoscopy using magnifying instruments have been devised to improve their identification [40]. Improvement of advanced software that is currently being developed in computer-aided diagnosis systems may allow fine detection of colonic wall thickening that even optical endoscopy may miss, and preliminary results are quite encouraging [23–25]. Another important issue is represented by the size threshold of 5 to 10 mm because the diagnostic accuracy of CTC for smaller lesions still seems to be unsatisfactory. On the one hand, false-positive results may induce too many unnecessary colonoscopies with increases in cost, risks, and patient discomfort; on the other, a high false-negative rate may cause small sessile adenomas with significant growth potential to be missed, such as serrated or small high-grade dysplasia adenomas. High-risk patients may harbor such lesions in their colon more frequently, and the effect of this limit should be properly addressed. There is no direct evidence in the literature on which to base the timing of repeat screening CTC. Based on known diagnostic values of CTC for polyps of different sizes, data in the literature on the growth of adenomas according to size, clinical experience, available guidelines for repeat CC screening, and the possibility CTC is somewhat less accurate than CC but more accurate than double contrast barium enema, Pickhardt [41] proposed that only patients in whom CTC detects a polyp larger than 1 cm in diameter be sent for polypectomy. He suggested that patients who have a polyp smaller than 1 cm not undergo CC; based on the progressively lower positive predictive value and specificity of CTC for such polyps, he suggested follow-up CTC at 1, 2, and 5 years when estimated polyp sizes are 8 to 9 mm, 6 to 7 mm, and smaller than 6 mm, respectively. We believe this algorithm may be a valid and cost-effective proposal for low- to average-risk patients in a widespread screening program, provided that such an approach be considered a working hypothesis and its safety and cost effectiveness be first tested in carefully designed prospective controlled studies for its obvious ethical and scientific implications. When dealing with high-risk patients, this approach may not be satisfactory because these people have a higher likelihood of advanced and, hence, more aggressive subcentimeter lesions compared with the general population at average risk, and higher rates of clinically significant lesions such as flat adenomas are still beyond the diagnostic capacity of CTC. For these reasons,

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in high-risk patients, we suggest that polyps in the diagnostic gray area of 6 to 9 cm should trigger the indication for CC [35], although the number of negative colonoscopies due to a false-positive finding on CTC likely would increase significantly. The concern for a possible increase in serious complications, unjustified by the expected benefit of polypectomy according to Pickardt, may not be substantial. Such an approach is in effect likely to generate, on the one hand, a larger number of small lesions whose complication rate is expected to be minimal and, on the other, detection of flat lesions at high risk of malignant degeneration for which endoscopic resection is considered mandatory despite the inherent risk of complications. Further, it should be remembered that all available guidelines have indicated that the interval between screening colonoscopies should be greatly decreased in high-risk patients in whom premalignant lesions are expected to have a faster growth rate. Thus, the 5-year interval suggested for CTC when small polyps are diagnosed in average-risk patients may not be adequate in those at high risk. Another hot topic of discussion for CTC is the risk of radiation exposure, which is of concern because the screening test is expected to be repeated several times in the patient’s life. This issue is obviously less relevant in symptomatic patients for whom the risk is clearly negligible by comparison with the benefit of the examination; in contrast, in asymptomatic people, the benefit may not be so evident if a ‘‘negative’’ finding on CTC needs a follow-up confirmation in a few years’ time. An exhaustive review has been recently published by van Gelder et al. [42] who recommended that low- and ultra-low-dose protocols be mandatory when CTC is included in a screening program because using the routine standard doses of 4 to 12 mSv in patients 50 years of age implies an estimated risk of causing a fatal cancer, which varies between 1:10,000 and 1:3500, respectively, and may not be acceptable particularly in view of the need for repeating the examination several times in each individual [43] There are several studies in which various dose ranges have been compared, from the standard of 12 mSV to the ultra low of 1.7 mSv [44–46]; these studies have shown that accuracy values do not vary significantly, thus lending support for a confident use of ultra-low-dose protocols that are thus likely to offset the potential risk of repeat CTC screening, particularly concerning highrisk patients. Measuring the cost of CTC and calculating its cost efficacy is not an easy task because of the rapidly evolving technology for CT scanners and software. It is also difficult to generalize the estimates in contrast with endoscopic examinations because the equipment is not universally dedicated to performing CTC and the type of tests may vary according to patients’ characteristics. Sonnenberg et al. in 1999 calculated that for CTC screening to have a cost efficiency similar to that of CC,

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using the same intervals between tests, adherence to the program should exceed that usually observed for CC by 15% to 20% and CTC should cost 54% less than CC [47]. This careful estimate deserves some further comments. By screening high-risk patients with CTC, the number of colonoscopies induced by positive findings as described previously would be expected to be larger than that for average-risk patients, after determining a probable further decreased in cost efficacy. In contrast, if the usually very low, 30% at best, compliance to screening these patients is dramatically increased by the attractiveness of CTC on the target population to the levels attained by screening programs for breast and uterine cancers, this approach may positively affect the cost efficacy ratio.

Conclusion Considering the currently evolving technologic field of CTC, we believe that it would be wiser to keep an open mind in terms of its use in screening programs. For this reason, we strongly feel that large and well-conducted trials in high-risk patients should be carried out to clarify the possible screening role of CTC. Particular attention should be given to its cost efficacy, whose key factor for obtaining a favorable ratio is, in our opinion, the compliance of the target population in view of the enormous economic, social, and emotional advantages that would result from any program capable of further decreasing the number of deaths from CRC. References 1. Bray F, Sankila R, Ferlay J, Parkin DM (2002) Estimates of cancer incidence and mortality in Europe in 1995. Eur J Cancer 38:99–166 2. Smith RA, Cokkinides V, von Eschenbach AC, et al. (2002) American Cancer Society guidelines for the early detection of cancer. CA Cancer J Clin 52:8–22 3. Winawer SJ, Fletcher RH, Rex D, et al. (2003) Colorectal screening and surveillance: clinical guidelines rationale—update based on new evidence. Gastroenterology 124:544–560 4. Wagner JL, Tunis S, Brown M, et al. (1996) The cost-effectiveness of colorectal cancer screening in average-risk adults. In: Young G, Levin B, Rozen A, (eds) Prevention and early detection of colorectal cancer. London: WB Saunders, pp 321–256 5. Lynch HT, de la Chapelle A (2003) Hereditary colorectal cancer. N Engl J Med 348:919–932 6. Fuchs CS, Giovannucci EL, Colditz GA, et al. (1994) A prospective study of family history and the risk of colorectal cancer. N Engl J Med 331:1669–1674 7. Winawer SJ, Zauber AG, Gerdes H, et al. (1996) Risk of colorectal cancer in the families of patients with adenomatous polyps National Polyp Study Workgroup. N Eng J Med 334:82–87 8. Henry LG, Condon RE, Schulte WJ, et al. (1975) Risk of recurrence of colon polyps. Ann Surg 182:511–515 9. Kirsner JB, Rider JA, Moeller HC, et al. (1960) Polyps of the colon and rectum: statistical analysis of a long-term follow-up study. Gastroenterology 39:178–182 10. Waye JD, Braunfeld SF (1982) Surveillance intervals after colonoscopic polypectomy. Endoscopy 14:79–81 11. Fowler DL, Hedberg SE (1980) Follow-up colonoscopy after polypectomy [abstract]. Gastrointest Endosc 26:67 12. Matek W, Guggenmoos-Holzman I, Demling L (1985) Follow-up of patients with colorectal adenomas. Endoscopy 17:175–181

13. Atkin WS, Morson BC, Cuzick J (1992) Long-term risk of colorectal cancer after excision of rectosigmoid adenomas. N Engl J Med 326:658–662 14. Gillespie PE, Chambers RJ, Chan KW, et al. (1979) Colonic adenomas: a colonoscopy survey. Gut 20:240–245 15. Winawer S, Zauber AG, O’Brien MJ, et al. (1993) Randomized comparison of surveillance intervals after colonoscopic removal of newly diagnosed adenomatous polyps. N Engl J Med 328:901–906 16. Van Stolk RU, Beck GJ, Baron JA, et al. (1998) Adenoma characteristics at first colonoscopy as predictors of adenoma recurrence and characteristics at follow-up. Gastroenterology 115:13–18 17. Zauber AG, Winawer SJ (1997) Initial management and follow-up surveillance of patients with colorectal adenomas. Gastroenterol Clin North Am 26:85–101 18. Choi PM, Nugent FW, Schoetz DJJ, et al. (1993) Colonoscopic surveillance reduces mortality from colorectal cancer in ulcerative colitis. Gastroenterology 105:418–424 19. Citarda F, Tomaselli G, Capocaccia R, et al. (2001) The Italian Multicentre Study Group. Efficacy in standard clinical practice of colonoscopic polypectomy in reducing colorectal cancer incidence. Gut 48:812–815 20. Gatto NM, Frucht H, Sundararajan V, et al. (2003) Risk of perforation after colonoscopy and sigmoidoscopy: a population-based study. J Natl Cancer Inst 95:230–236 21. Vining DJ, Gelfand DW, Bechtold RE, et al. (1994) Technical feasibility of colon imaging with helical CT and virtual reality [abstract]. AJR 62(suppl 104):104a 22. Halligan S, Fenlon HM (1999) Virtual colonoscopy. BMJ 319(7219):1249–1252 23. Summers RM, Jerebko AK, Franaszek M, et al. (2002) Colonic polyps: complementary role of computer-aided detection in CT colonography. Radiology 225:391–399 24. Yoshida H, Nappi J, MacEneaney P, et al. (2002) Computer-aided diagnosis scheme for detection of polyps at CT colonography. Radiographics 22:963–979 25. Kiss G, Van Cleynenbreugel J, Thomeer M, et al. (2002) Computeraided diagnosis in virtual colonography via combination of surface normal and sphere fitting methods. Eur Radiol 12:77–81 26. Johnson CD, Ahlquist DA (1999) Computed tomography colonography (virtual colonoscopy): a new method for colorectal screening. Gut 44:301–305 27. Morrin MM, LaMont JT (2003) Screening virtual colonoscopy—ready for prime time? N Engl J Med 349:2261–2264 28. Johnson CD, Harmsen WS, Wilson LA, et al. (2003) Prospective blinded evaluation of computed tomographic colonography for screen detection of colorectal polyps. Gastroenterology 125:311–319 29. Yee J, Akerkar GA, Hung RK, et al. (2001) Colorectal neoplasia: performance characteristics of CT colonography for detection in 300 patients. Radiology 219:685–692 30. Spinzi G, Belloni G, Martegani A, et al. (2001) Computed tomographic colonography and conventional colonoscopy for colon diseases: a prospective, blinded study. Am J Gastroenterol 96:394–400 31. Gallo TM, Galatola G, Fracchia M, et al. (2003) Computed tomography colonography in routine clinical practice. Eur J Gastroenterol Hepatol 15:1323–1331 32. Sosna J, Morrin MM, Kruskal JB, et al. (2003) CT colonography of colorectal polyps: a metaanalysis. AJR 181:1593–1598 33. Pickhardt PJ, Choi JR, Hwang I, et al. (2003) Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med 349:2191–2200 34. Johnson CD, Harmsen WS, Wilson LA, et al. (2003) Prospective blinded evaluation of computed tomographic colonography for screen detection of colorectal polyps. Gastroenterology 125:311–319 35. Macari M, Bini EJ, Jacobs SL, et al. (2004) Colorectal polyps and cancers in asymptomatic average-risk patients: evaluation with CT colonography. Radiology 230:629–636 36. Cotton PB, Durkalski VL, Pineau BC, et al. (2004) Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA 291:1772–1774 37. Van Gelder RE, Nio CY, Florie J, et al. (2004) Computed tomographic colonography compared with colonoscopy in patients at increased risk for colorectal cancer. Gastroenterology 127:41–48

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38. Fenlon HM, Nunes DP, Schroy PC III, et al. (1999) A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 341:1496–1503 39. Hurlstone DP, Cross SS, Adam I, et al. (2003) A prospective clinicopathological and endoscopic evaluation of flat and depressed colorectal lesions in the United Kingdom. Am J Gastroenterol 98:2543–2549 40. Hurlstone DP, Cross SS, Adam I, et al. (2004) Efficacy of high magnification chromoscopic colonoscopy for the diagnosis of neoplasia in flat and depressed lesions of the colorectum: a prospective analysis. Gut 53:284–290 41. Pickhardt PJ (2005) CT colonography (virtual colonoscopy) for primary colorectal screening: challenges facing clinical implementation. Abdom Imaging 30:1–4 42. van Gelder RE, Florie J, Stoker J (2005) Colorectal cancer screening and surveillance with CT colonography: current controversies and obstacles. Abdom Imaging 30:5–12

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43. 1990 Recommendations of the International Commission on Radiological Protection. In: Smith H, (ed). Annals of the ICRP 21 (nos. 1–3). International Commission on Radiological Protection publication 60. Oxford: Pergamon Press, 1991 44. van Gelder RE, Venema HW, Serlie IW, et al. (2002) CT colonography at different radiation dose levels: feasibility of dose reduction. Radiology 224:25–33 45. Iannaccone R, Laghi A, Catalano C, et al. (2003) Feasibility of ultra-low-dose multislice CT colonography for the detection of colorectal lesions: preliminary experience. Eur Radiol 13:1297– 1302 46. van Gelder RE, Venema HW, Florie J, et al. (2004) CT colonography: feasibility of substantial dose reduction—comparison of medium to very low doses in identical patients. Radiology 232:611–620 47. Sonnenberg A, Delco F, Bauerfeind P (1999) Is virtual colonoscopy a cost-effective option to screen for colorectal cancer? Am J Gastroenterol 94:2268–2274