Correspondence
CT Colonography versus Colonoscopy for the Detection of Advanced Neoplasia
N Engl J Med 2008; 358:88-90January 3, 2008
- Article
To the Editor:
We raise two issues regarding the nonrandomized comparison of computed tomographic colonography (CTC) and optical colonoscopy (OC) reported by Kim et al. (Oct. 4 issue).1 First, the prevalence of cancer in the OC group (0.1%) was 10 to 20% of the expected prevalence, whereas the prevalence of cancer in the CTC group was more consistent with that in a screening population.2,3 Since the symptom prevalence in the groups was equal, the unequal cancer prevalence suggests that the OC group had more patients with prior negative screening, which is associated with low rates of cancer and advanced adenomas.4 The surprising finding of a higher prevalence of flat adenomas in the CTC group supports the nonequivalence of the two groups. We welcome clarification about prior screening endoscopy in the two groups, as well as an explanation for the higher rates of cancer and flat-adenoma detection in the CTC group.
Second, an assessment of the quality of the OC examinations would be useful, including cecal-intubation rates, the overall prevalence of adenomas detected by OC, and the number of colonoscopists who achieved minimum recommended thresholds for adenoma detection.5
Douglas K. Rex, M.D.
Thomas F. Imperiale, M.D.
Indiana University, Indianapolis, IN 46202
drex@iupui.edu Dr. Rex reports receiving research support from Olympus. No other potential conflict of interest relevant to this letter was reported.
5 References1
Kim DH ,Pickhardt PJ ,Taylor AJ , et al. CT colonography versus colonoscopy for the detection of advanced neoplasia. N Engl J Med 2007;357:1403-1412
Full Text | Web of Science | Medline2
Lieberman DA ,Weiss DG ,Bond JH ,Ahnen DJ ,Garewal H ,Chejfec G . Use of colonoscopy to screen asymptomatic adults for colorectal cancer. N Engl J Med 2000;343:162-168[Erratum, N Engl J Med 2000;343:1204.]
Full Text | Web of Science | Medline3
Regula J ,Rupinski M ,Kraszewska E , et al. Colonoscopy in colorectal-cancer screening for detection of advanced neoplasia. N Engl J Med 2006;355:1863-1872
Full Text | Web of Science | Medline4
Rex DK ,Cummings OW ,Helper DJ , et al. 5-Year incidence of adenomas after negative colonoscopy in asymptomatic average-risk persons. Gastroenterology 1996;111:1178-1181
CrossRef | Web of Science | Medline5
Rex DK ,Petrini JL ,Baron TH , et al. Quality indicators for colonoscopy. Gastrointest Endosc 2006;63:Suppl:S16-S28
CrossRef | Web of Science | Medline
To the Editor:
Kim et al. report that the two screening programs they compared, one based on CTC and the other on OC, had a similar diagnostic yield, with more complications in the OC group. Before these findings can be used to guide screening recommendations, some important questions should be answered. Putting aside a potential selection bias due to nonrandomized assignment of subjects to the study groups, one major concern is the quality of colonoscopy used in the study. First, data on important quality indexes, such as the cecal-intubation rate, the adenoma-detection rate, and bowel preparation, were not provided. Second, the 0.2% perforation rate in the OC group is much higher than that reported in other screening studies (0 to 0.05%).1-4 Third, the rate of advanced-neoplasia detection and especially the rate of colorectal-cancer detection (3.4% and 0.1%, respectively) in the OC group are much lower than those previously reported.1-4 Given these reservations, one cannot exclude the possibility that what the study actually compared was top-notch CTC and suboptimal OC.
4 ReferencesJaroslaw Regula, M.D.
M. Sklodowska-Curie Memorial Cancer Center, 02-781 Warsaw, Poland
jregula@coi.waw. pl Marcin Polkowski, M.D.
Medical Center for Postgraduate Education, 02-781 Warsaw, Poland1
Regula J ,Rupinski M ,Kraszewska E , et al. Colonoscopy in colorectal-cancer screening for the detection of advanced neoplasia. N Engl J Med 2006;355:1863-1872
Full Text | Web of Science | Medline2
Lieberman DA ,Weiss DG ,Bond JH ,Ahnen DJ ,Garewal H ,Chejfec G . Use of colonoscopy to screen asymptomatic adults for colorectal cancer. N Engl J Med 2000;343:162-168[Erratum, N Engl J Med 2000;343:1204.]
Full Text | Web of Science | Medline3
Imperiale TF ,Wagner DR ,Lin CY ,Larkin GN ,Rogge JD ,Ransohoff DF . Risk of advanced proximal neoplasms in asymptomatic adults according to the distal colorectal findings. N Engl J Med 2000;343:169-174
Full Text | Web of Science | Medline4
Strul H ,Kariv R ,Leshno M , et al. The prevalence rate and anatomic location of colorectal adenoma and cancer detected by colonoscopy in average-risk individuals aged 40-80 years. Am J Gastroenterol 2006;101:255-262
CrossRef | Web of Science | Medline
To the Editor:
Adoption of the suggestion by Kim et al. that colon-cancer screening can be effectively and safely accomplished by CT scanning would lead to higher-than-ever CT-scanning rates in the United States. Nowhere in the article do the authors mention the radiation dose that patients are exposed to by such studies. According to a report by the National Academy of Sciences, a single population dose of 10 mSv is associated with a lifetime risk of a solid cancer or leukemia of 1 in 2000.1 The radiation dose associated with a typical abdominal CT scan is 10 to 20 mSv.2 It is particularly problematic when patients have multiple CT scans.2 Some authors now suggest that informed consent be obtained when patients are to be exposed to these levels of radiation.3 Kim et al. should at least acknowledge these concerns.
3 ReferencesDavid S. Glaser, M.D.
Exempla St. Joseph Hospital, Denver, CO 80218
glaserd@exempla.org 1
Martin DR ,Semelka RC . Health effects of ionising radiation from diagnostic CT. Lancet 2006;367:1712-1714[Erratum, Lancet 2006;368:1494.]
CrossRef | Web of Science | Medline2
Katz SI ,Saluja S ,Brink JA ,Forman HP . Radiation dose associated with unenhanced CT for suspected renal colic: impact of repetitive studies. AJR Am J Roentgenol 2006;186:1120-1124
CrossRef | Web of Science | Medline3
Picano E . Informed consent and communication of risk from radiological and nuclear medicine examinations: how to escape from a communication inferno. BMJ 2004;329:849-851
CrossRef | Web of Science | Medline
To the Editor:
CTC has the potential to complement current technology in evaluating the colon, as highlighted in the report by Kim and colleagues. However, the practice of following, rather than removing, polyps that are 6 to 9 mm may lead to missed lesions, including cancers, thereby lessening the impact of true prevention (rather than early detection) with colorectal-cancer screening.
Four prior studies have demonstrated more than a 12% combined prevalence of histologically advanced lesions among more than 6000 adenomas that were 5 to 10 mm, with almost 1% of those lesions containing frank cancer.1-4 In fact, one prior study showed a 15.5% prevalence of histologically advanced lesions among adenomas that were 5 to 9 mm.2 The size of individual polyps in one of these large studies was assessed by multiple methods to ensure accuracy.1
Thus, the finding in the study by Kim et al. of a 0.2% prevalence of subcentimeter advanced neoplasias conflicts with the results of multiple prior studies. Choosing to leave polyps that are 6 to 9 mm in place may be a risky approach to cancer prevention.
4 ReferencesLynn F. Butterly, M.D.
Dartmouth–Hitchcock Medical Center, Lebanon, NH 03756
lynn.butterly@dartmouth. edu Heiko Pohl, M.D.
Veterans Affairs Hospital, White River Junction, VT 050091
Butterly LF ,Chase MP ,Pohl H ,Fiarman GS . Prevalence of clinically important histology in small adenomas. Clin Gastroenterol Hepatol 2006;4:343-348
CrossRef | Web of Science | Medline2
Shinya H ,Wolff WI . Morphology, anatomic distribution and cancer potential of colonic polyps. Ann Surg 1979;190:679-683
CrossRef | Web of Science | Medline3
O'Brien MJ ,Winawer SJ ,Zauber AG , et al. The National Polyp Study: patient and polyp characteristics associated with high grade dysplasia in colorectal adenomas. Gastroenterology 1990;98:371-379
Web of Science | Medline4
Gschwantler M ,Kriwanek S ,Langner E , et al. High-grade dysplasia and invasive carcinoma in colorectal adenomas: a multivariate analysis of the impact of adenoma and patient characteristics. Eur J Gastroenterol Hepatol 2002;14:183-188
CrossRef | Web of Science | Medline
Author/Editor Response
Rex and Imperiale question the differences in detected cancers and flat lesions between the CTC and OC groups. For flat lesions, the explanation probably resides in subjective classification differences rather than actual population differences. In our experience, many lesions that are labeled flat at CTC are called sessile at OC. The difference in cancer detection was more unexpected and difficult to explain. Rex and Imperiale suggest differences in prior screening. Our series represent young, average-risk members of screening populations, nearly half of whom are 55 years of age or younger. If any prior screening occurred, it would be negligible and would probably cancel out between the cohorts. Even if there were a substantive difference, it should also result in differences in advanced adenomas, which was not the case. One possible explanation is a difference in cancer-detection capabilities. In the prior Department of Defense trial, in which the same group of patients underwent both screening approaches, CTC detected both cancers, whereas OC missed one.1 Similarly, in a recent Mayo Clinic study, CTC detected all cancers, whereas OC missed four of five cancers.2 Longitudinal follow-up of our study population for future cancer rates may shed more light on this issue.
Regula and Polkowski suggest that CTC is similar to OC when OC is performed suboptimally. It is unfortunate that the results of this study would lead some to impugn the capabilities of the colonoscopists. They are highly trained, experienced university gastroenterologists. The mean cecal-intubation rate for the 10 endoscopists was 98% (range, 92 to 100). The perforation rate has been used unfairly to indicate poor quality. As for the capabilities of state-of-the-art CTC, the sensitivity is similar to that of high-quality OC, as repeatedly demonstrated in the recent American College of Radiology Network study (ACRIN 6664), the Italian Multicenter Polyp Accuracy CTC (IMPACT) study, and the Munich Colorectal Cancer Prevention trial.
Glaser calls attention to patients' radiation exposure. He echoes the concern of others regarding the cancer risks associated with the use of CT.3 However, properly performed CTC is a very-low-dose examination, calculated at about 2.5 mSv per series. The most recent Health Physics Society position statement reports that at such a low dose, the risk cannot be reliably quantified and may be nonexistent.4 Even proponents of the linear, no-threshold model of risk concede that the benefit–risk ratio is large for colorectal-cancer screening by CTC.5
Butterly and Pohl note that our reported prevalence of advanced histologic findings in small polyps conflicts with the results of older studies involving higher-risk populations. More important, however, is the fact that our finding is in concert with newer colonoscopy data in true screening populations. A recent study of 6694 resected colorectal neoplasms that were 5 to 10 mm in size revealed only 2 malignant polyps (0.030%).6 In another large colonoscopy study, involving a screening cohort of 13,714 adults, the reported prevalence of 6-to-9-mm cancers was 0.015%.7 Furthermore, surveillance of 5-to-9-mm polyps at a 3-year interval has been shown to be a safe strategy,8 suggesting a clear benefit of decreasing polypectomies of low yield. This practice falls well within the precedent set for mammographic surveillance of lesions that are likely to be benign — that is, the chance that the lesion is cancerous is 2% or lower, and cancers detected at surveillance are early-stage cancers (stage I).
8 ReferencesDavid H. Kim, M.D.
Perry J. Pickhardt, M.D.
University of Wisconsin Medical School, Madison, WI 53792-3252
dkim@uwhealth.org 1
Pickhardt PJ ,Choi JR ,Hwang I , et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med 2003;349:2191-2200
Full Text | Web of Science | Medline2
Johnson CD ,Fletcher JG ,MacCarty RL , et al. Effect of slice thickness and primary 2D versus 3D virtual dissection on colorectal lesion detection at CT colonography in 452 asymptomatic adults. AJR Am J Roentgenol 2007;189:672-680
CrossRef | Web of Science | Medline3
Brenner DJ ,Hall EJ . Computed tomography -- an increasing source of radiation exposure. N Engl J Med 2007;357:2277-2284
Full Text | Web of Science | Medline4
Radiation risk in perspective: position statement of the Health Physics Society. Adopted January 1996, revised August 2004. McLean, VA: Health Physics Society, 2004. (Accessed December 3, 2007, at http://www.hps.org/documents/radiationrisk.pdf.)
5
Brenner DJ ,Georgsson MA . Mass screening with CT colonography: should the radiation exposure be of concern? Gastroenterology 2005;129:328-337
CrossRef | Web of Science | Medline6
Sprung D . Prevalence of adenocarcinoma in small adenomas. Am J Gastroenterol 2006;101:S199-S199
Web of Science7
Moravec M ,Lieberman DA ,Holub J ,Michaels L ,Eisen GM . Rate of advanced pathologic features in 6-9 mm polyps in patients referred for colonoscopy screening. Gastrointest Endosc 2007;65:AB127-AB127
CrossRef | Web of Science8
Hofstad B ,Vatn MH ,Andersen SN , et al. Growth of colorectal polyps: redetection and evaluation of unresected polyps for a period of three years. Gut 1996;39:449-456
CrossRef | Web of Science | Medline
- Citing Articles (3)
Citing Articles
1
Roy Soetikno, Tonya Kaltenbach. (2010) High-quality CT Colonography Can Detect Nonpolypoid Colorectal Neoplasm (NP-CRN)—Science or Rhetoric?. Academic Radiology 17:10, 1317
CrossRef2
Ifigeneia Mavranezouli, James E. East, Stuart A. Taylor. (2008) CT colonography and cost-effectiveness. European Radiology 18:11, 2485-2497
CrossRef3
Anna M. Buchner, Michael B. Wallace. (2008) Future expectations in digestive endoscopy: Competition with other novel imaging techniques. Best Practice & Research Clinical Gastroenterology 22:5, 971-987
CrossRef
