Influence of Updated Colorectal Cancer Screening Guideline

The recent publication of the updated Joint Colorectal Cancer Screening Guideline1 by the American Cancer Society (ACS), the U.S. Multisociety Task Force (MSTF) on Colorectal Cancer, and the American College of Radiology (ACR) might seem to be a collaboration of strange bedfellows, but such an alliance is not an entirely novel undertaking. Formed in 2000 and consisting of representatives from the American College of Gastroenterology, the American Gastroenterological Association, the American Society for Gastrointestinal Endoscopy (ASGE), and the American College of Physicians (ACP), the MSTF previously collaborated with the ACS on postpolypectomy surveillance and postcancer resection surveillance guidelines that were published in 2006.2 The MSTF issued its first guidelines on colorectal cancer (CRC) screening in 2003, and those guidelines3 were endorsed by a number of groups, including the ACR. Groups representing different specialties collaborate in the formulation of screening guidelines, partly in an effort to create an aura of consensus around such guidelines, which one hopes will serve as a powerful endorsement for screening in the minds of both primary care physicians and patients.

The updated Joint Colorectal Cancer Screening Guideline focuses only on screening. One new element of this guideline is the division of screening tests into cancer detection tests (primarily stool-based tests) and cancer prevention tests (imaging tests capable of detecting both adenomas and polyps). The guideline specifically recommends that practitioners emphasize the importance of cancer prevention tests to patients.

The real news in the updated guideline is the inclusion of fecal DNA testing and computed tomography colonography in the “menu-of-options” approach to colorectal cancer screening; this approach was first presented by the GI Consortium in 1997 and was adopted immediately by the ACS. The menu-of-options concept assumes that, because CRC screening tests differ in effectiveness, cost, risk, and invasiveness (and, therefore, acceptability), no single test is optimal for every situation. Thus, physicians should discuss the pros and cons of each test with their patients, and, together, they should choose a screening test that suits their priorities and that will be paid for by the patients’ insurance companies. One advantage of this approach is that it increases the available testing options for physicians and patients. A disadvantage is that it can create confusion, particularly as the number of available tests now has gone from four (colonoscopy, sigmoidoscopy, double-contrast barium enema [DCBE], and fecal occult blood tests [FOBT]) to six (fecal DNA testing and CT colonography have been added). Although the ACG and the ASGE have endorsed the menu-of-options guideline, both organizations also have their own guidelines that recommend colonoscopy as the preferred CRC screening strategy. A prospective trial of whether the menu-of-options approach or the colonoscopy-preferred approach is most likely to result in screening would be beneficial.

We know that 30% to 40% of the general population will not accept any form of invasive testing or bowel preparation required for testing; thus, making noninvasive testing available to these individuals is important. In the long term, availability of blood-based testing for CRC screening is considered the “Holy Grail” for this group of patients. The first such tests to become available likely will be based on gene hypermethylation or on proteomics and probably will be designed primarily for detecting cancer, rather than adenomas. Therefore, the tests would be most appropriate for patients who decline colonoscopy or another imaging modality. In the interim, we must use stool-based tests for this group of patients. The updated Joint Colorectal Cancer Screening Guideline makes firm recommendations that Hemoccult II card tests should be abandoned in favor of fecal immunochemical testing (FIT) or Hemoccult Sensa tests. These two newer tests clearly outperform the older guaiac-based Hemoccult II card test, and they are inexpensive. Gastroenterologists who are educating their referring primary care physicians should recommend FOBT and should encourage hospital clinical laboratories to install FIT assay systems. The new guideline’s endorsement of fecal DNA testing is consistent with the menu-of-options philosophy but likely will be controversial. The guideline suggested no specific interval for fecal DNA testing, and this omission will create confusion in clinical practice and probably will cause some overuse of a relatively expensive test. In addition, common sense would suggest that FIT should outperform DNA testing and would cost much less.

The inclusion of CT colonography in the Joint Colorectal Cancer Screening Guideline is also likely to be controversial. The menu-of-options philosophy made it inevitable that CT colonography would be included in the updated guideline, particularly since DCBE, which already was included in the guideline, is less effective than CT colonography and less acceptable to patients. Although CT colonography is more expensive than DCBE, its estimated cost-effectiveness as a screening test falls within acceptable thresholds. The guideline authors’ willingness to endorse CT colonography was influenced by the principal findings of the American College of Radiology Imaging Network (ACRIN) Trial 6664, also called the National CT Colonography Trial. The preliminary results of this trial indicated that CT colonography detected 90% of polyps ≥1 cm, a result that exceeds the detection rate of DCBE and rivals that of conventional colonoscopy. The challenges for CT colonography continue to be management of small polyps, radiation risk, cost and management of extracolonic findings, and the question of whether the overall cost will be acceptable to payers. Data from the ACRIN trial also indicated that CT colonography’s specificity for large adenomas was only 86%, and its positive predictive value was 23%. These limitations will result in lengthy and costly colonoscopies to rule out false-positive lesions detected by CT colonography. The CTC Category 1 code for screening using CT colonography is unlikely to become available before early 2010. During the interim, individual gastroenterologists and gastroenterologic organizations must decide about the adoption of CT colonography.

I remain unconvinced that CT colonography will have a positive influence on CRC prevention, and cancer prevention in general, in the U.S. The single most important question about CT colonography is whether it will increase adherence to screening, and we have no reliable evidence showing that it will. If CT colonography does increase adherence, it should lead to detection of large polyps in many patients, and colonoscopy and resection of those polyps should help to prevent CRCs. If CT colonography primarily displaces patients from colonoscopy, then polypectomy rates could fall and CRC incidence rates could rise. Gastroenterologists are best suited to decide which patients could benefit from screening with CT colonography (ideally, patients with low preprocedure probability of polyps) and which patients with polyps on CT colonography should undergo colonoscopy; they also are in the best position to inform patients about the relative risks of colonoscopy and CT colonography, including the radiation risk associated with the latter. If CT colonography enters more-widespread use, monitoring its effects on adherence to screening, CRC prevention, polypectomy rates, and colonoscopy complications will be critically important. Until we know CT colonography’s effect on those factors, we cannot know whether it will have a positive influence on CRC prevention in the U.S.