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Task Force Issues Guidelines on Screening for Colorectal Cancer

Most harms result from use of colonoscopy

The U.S. Preventive Services Task Force (USPSTF) has released a final recommendation statement on screening patients for colorectal cancer. The guidelines pertain to adults 50 to 85 years of age.

The group recommends screening for colorectal cancer starting at age 50 years and continuing until age 75 years. The risks and benefits of different screening methods vary.

The decision to screen for colorectal cancer in adults aged 76 to 85 years should be an individual one, taking into account the patient’s overall health and screening history. Adults in this age group who have never been screened for colorectal cancer are more likely to benefit. Screening would be most appropriate among adults who 1) are healthy enough to undergo treatment if colorectal cancer is detected and 2) do not have comorbid conditions that would significantly limit their life expectancy.

The recommendations apply to asymptomatic adults 50 years of age and older who are at average risk of colorectal cancer and who do not have a family history of known genetic disorders that predispose them to a high lifetime risk of colorectal cancer (such as Lynch syndrome or familial adenomatous polyposis), a personal history of inflammatory bowel disease, a previous adenomatous polyp, or previous colorectal cancer.

The USPSTF found convincing evidence that screening for colorectal cancer in adults 50 to 75 years of age reduces colorectal cancer mortality. The task force also found no head-to-head studies demonstrating that any of the screening strategies it considered were more effective than others.

The benefit of early detection of and intervention for colorectal cancer declines after age 75 years, according to the guidelines. Among older adults who have been previously screened for colorectal cancer, there is at best a moderate benefit to continuing screening during the ages of 76 to 85 years. However, adults in this age group who have never been screened for colorectal cancer are more likely to benefit than are those who have been previously screened.

To date, no method of screening for colorectal cancer has been shown to reduce all-cause mortality in any age group.

The USTSPF determined that the harms of screening for colorectal cancer in adults aged 50 to 75 years are small. Most harms result from the use of colonoscopy, either as the screening test or as follow-up for positive findings detected by other screening tests. The rate of serious adverse events from colorectal cancer screening increases with age. Therefore, the harms of screening for the disease in adults 76 years of age and older are small-to-moderate, the task force found.

Randomized clinical trials have shown that screening with the guaiac-based fecal occult blood test (gFOBT) reduces colorectal cancer deaths. Studies have also shown, however, that fecal immunochemical tests (FITs), which identify intact human hemoglobin in stool, have improved sensitivity compared with that of gFOBT for detecting colorectal cancer. Among the FITs that are cleared by the FDA and are available for use in the United States, the OC FIT-CHEK family of FITs (Polymedco) have the best test performance characteristics (i.e., the highest sensitivity and specificity), according to the USTSPF. Multitargeted stool DNA testing (FIT-DNA) is an emerging screening strategy that combines a FIT with testing for altered DNA biomarkers in cells shed into the stool. Multitargeted stool DNA testing has increased single-test sensitivity for detecting colorectal cancer compared with FIT alone.

The harms of stool-based testing primarily result from adverse events associated with follow-up colonoscopy of positive findings. The specificity of FIT-DNA is lower than that of FIT alone, which means that it has a higher number of false–positive results and a higher likelihood of follow-up colonoscopy and of experiencing an associated adverse event per screening test.

Several studies have shown that flexible sigmoidoscopy alone reduces deaths from colorectal cancer. Flexible sigmoidoscopy combined with FIT was studied in a single trial and was found to reduce the colorectal cancer-specific mortality rate compared with flexible sigmoidoscopy alone.

Flexible sigmoidoscopy can result in direct harms, such as colonic perforations and bleeding, although the associated event rates are much lower than those observed with colonoscopy. Harms can also occur as a result of follow-up colonoscopy.

Colonoscopy has both indirect and direct harms. Harms may be caused by bowel preparation before the procedure (e.g., dehydration and electrolyte imbalances), the sedation used during the procedure (e.g., cardiovascular events), or the procedure itself (e.g., infection, colonic perforations, or bleeding).

Evidence for assessing the effectiveness of computed tomography (CT) colonography is limited to studies of its test characteristics, the task force noted. CT colonography can result in unnecessary diagnostic testing or treatment of incidental extracolonic findings that are of no importance or that would never have threatened the patient’s health or become apparent without screening (i.e., overdiagnosis and overtreatment). As with other screening strategies, indirect harms from CT colonography can also occur from follow-up colonoscopy for positive findings.

Source: USPSTF; June 2016.

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