Colorectal Cancer: Screening and Surveillance Recommendations

sDNA

Fecal DNA testing uses knowledge of molecular genomics and provides the basis of a new method of CRC screening that tests stool for the presence of known DNA alterations in the adenoma-carcinoma sequence of colorectal carcinogenesis [11]. Three different types of fecal DNA testing kits have been evaluated. The sensitivity for cancer in each version was superior to traditional guaiac-based occult blood testing, but the sensitivities ranged from 52%–87%, with the specificities ranging from 82%–95%. Based on the accumulation of evidence since the last update of joint guideline, the joint guideline panel concluded that there now are sufficient data to include sDNA as an acceptable option for CRC screening [11].

As for overall recommendations for stool-based testing, the ACG supports the joint guideline recommendation that older guaiac-based fecal occult blood testing be abandoned as a method for CRC screening. Because of more extensive data (compared with Hemoccult Sensa), and the high cost of fecal DNA testing, the American College of Gastroenterology recommends FIT as the preferred cancer detection test in cases where colonoscopy is not an option [43].

Invasive Tests Other than Colonoscopy

The use of flexible sigmoidoscopy for CRC screening is supported by high-quality case-control and cohort studies [46]. The chief advantage of flexible sigmoidoscopy is that it can be performed with a simple preparation (2 enemas), without sedation, and by a variety of practitioners in diverse settings. The main limitation of the procedure is that it does not examine the entire colon but only the rectum, sigmoid, and descending colon. The effectiveness of a flexible sigmoidoscopy program is based on the assumption that if an adenoma is detected during the procedure, the patient would be referred for colonoscopy to examine the entire colon.

DCBE is an imaging modality which can evaluate the entire colon in almost all cases and can detect most cancers and the majority of significant polyps. However, the lower sensitivity for significant adenomas when compared with colonoscopy may result in less favorable outcomes regarding CRC morbidity and mortality. Double-contrast barium enema is no longer recommended as an alternative CRC prevention test because its use has declined dramatically and also as its effectiveness for polyp detection is less than CT colonography [43].

CT Colonography

CT colonography every 5 years is endorsed as an alternative to colonoscopy every 10 years because of its recent performance in the American College of Imaging Network Trial 6664 (also known as the National CT Colonography Trial) [59]. The principle performance feature that justifies inclusion of CT colonography as a viable alternative in patients who decline colonoscopy is that the sensitivity for polyps ≥ 1 cm in size was 90% in the most recent multicenter US trial [59]. In this study, 25% of radiologists who were tested for entry into the trial but performed poorly were excluded from participation, and thus lower sensitivity might be expected in actual clinical practice. CT colonography probably has a lower risk of perforation than colonoscopy in most settings, but for several reasons it is not considered the equivalent of colonoscopy as a screening strategy. First, the evidence to support an effect of endoscopic screening on prevention of incident CRC and mortality is overwhelming compared with that for CT colonography. Second, the inability of CT colonography to adequately detect polyps 5 mm and smaller, which constitutes 80% of colorectal neoplasms, and whose natural history is still not understood, necessitates performance of the test at 5-year rather than 10-year intervals [43]. Finally, false-positives are common, and the specificity for polyps ≥ 1 cm in size was only 86% in the National CT Colonography Trial, with a positive predictive value of 23% [59]. The American College of Gastroenterology recommends that asymptomatic patients be informed of the possibility of radiation risk associated with one or repeated CT colonography studies, though the exact risk associated with radiation is unclear [60,61].