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Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit

Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing continued...

Some studies have assessed how well virtual colonoscopy can detect colorectal polyps without a laxative prep. The question is of great importance for implementation because the laxative prep required by both conventional colonoscopy and virtual colonoscopy is considered a great disadvantage by patients. By tagging feces with iodinated contrast material ingested during several days prior to the procedure, investigators in one study were able to detect lesions larger than 8 mm with 95% sensitivity and 92% specificity.[67] The particular tagging material used in this study caused about 10% of patients to become nauseated; however, other materials are being assessed.

Another study [68] utilized low fiber diet, orally ingested contrast, and 'electronic cleansing', a process that subtracts tagged feces. CTC identified 91% of persons with adenomas 10 mm or larger, but detected fewer (70%) lesions greater than or equal to 8 mm. Patients who received both CTC and optical colonoscopy preferred CTC to optical colonoscopy (290 vs. 175). This study shows that CTC without a laxative prep detects small 1 cm lesions with high sensitivity and is acceptable to patients. Long-term utilization of CTC will depend on several issues including the frequency of follow-up exams that would be needed to detect smaller lesions that were undetected and may grow over time.

Extracolonic abnormalities are common in CT colonography. Fifteen percent of patients in an Australian series of 100 patients, referred for colonography because of symptoms or family history, were found to have extracolonic findings, and 11% of the patients needed further medical workups for renal, splenic, uterine, liver, and gallbladder abnormalities.[69] In another study, 59% of 111 symptomatic patients referred for clinical colonoscopy in a Swedish hospital between June 1998 and September 1999 were found to have moderate or major extracolonic conditions on CT colonography. CT colonography was performed immediately prior to colonoscopy and these findings required further evaluation. It is unstated to what extent the follow-up of these incidental findings benefited patients.[70]

Sixty-nine percent of 681 asymptomatic patients in Minnesota had extracolonic findings, of which 10% were considered to be highly important by the investigators, requiring further medical workup. Suspected abnormalities involved kidney (34), chest (22), liver (8), ovary (6), renal or splenic arteries (4), retroperitoneum (3), and pancreas (1);[71] however, the extent to which these findings will contribute to benefits or harms is uncertain. Two other studies, one large (n = 2,195) and one small (n = 136) examined the moderate or high importance of extracolonic findings from CTC. The larger study [72] found that 8.6% of patients had an extracolonic finding of at least moderate importance, while 24% of patients in the smaller study [73] required some evaluation for an extracolonic finding. The larger study found nine cancers from these evaluations, at a partial cost (they did not include all costs) of $98.56 per patient initially screened. The smaller study found no important lesions from evaluation, at a cost of $248 per person screened. Both of these estimates of cost are higher than previous studies have found. The extent to which any patients benefited from the detection of extracolonic findings is not clear. Because both of these studies were conducted in academic medical centers, the generalizability to other settings is also not clear. Neither of these studies examined the effect of extracolonic findings on patient anxiety and psychological function.

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