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Comparing Colorectal Cancer Screening Methods

There are a number of ways to screen people for cancers of the colon or rectum, but RCCA medical oncologists Julianne W. Childs, DO, and Avishek Kumar, MD, note that colonoscopy remains the “gold standard” for screening and that some other methods may not be suitable for people depending on their risk factors. The options include:

At-home stool testing. Screening at home can be performed by methods such as a DNA fecal immunochemical test (such as Cologuard®) or a standard fecal immunochemical test.    

At-home testing is less invasive and more convenient than other screening methods. But whereas a colonoscopy can be performed every 10 years for people with no risk factors for colorectal cancer and no evidence of polyps on first colonoscopy, the American Cancer Society recommends that at-home stool testing be done annually. Also, if the stool test results are suspicious, a follow-up colonoscopy will be needed.

Additionally, at-home stool testing is suitable only for people with no risk factors for colorectal cancer, while colonoscopy is recommended for people with one or more risk factors, Dr. Childs notes.

Colonoscopy. In colonoscopy, a slender flexible tube equipped with a light and small video camera is inserted through the anus and into the rectum. The video camera transmits a detailed image of the rectum and colon to a computer monitor. If needed, special instruments can be passed through the colonoscope to remove polyps or obtain samples of suspicious growths.

Patients need to refrain from eating for several hours to a day before a colonoscopy, and must drink a “bowel prep” formulation the evening before to induce bowel movements that will empty the colon. The colonoscopy procedure itself takes 15 to 30 minutes. However, because patients typically are either sedated or receive anesthesia they usually need to take a day off from work to rest following the procedure.

Dr. Childs and Dr. Kumar emphasize that while colonoscopy is somewhat more involved than other screening methods, it has been instrumental in detecting colorectal cancers early and in reducing deaths from those cancers.     

Virtual colonoscopy (also called CT colonography). With this screening method, a computer program combines computed tomography (CT) and X-ray technology to create a 3-dimensional image of the interior of the colon and rectum.

The test is less invasive than traditional colonoscopy, does not require sedation and is performed in about 15 minutes. Virtual colonoscopy might be suitable for people with “relative contraindications” to traditional colonoscopy – for example, if a person cannot tolerate the standard pre-colonoscopy bowel prep or is at heightened risk of bowel perforation because of a past surgery or a medical condition, Dr. Kumar says.

But virtual colonoscopy has its drawbacks, Dr. Kumar adds. For one, while the bowel prep is modified, it is still required. “You don’t get out of the prep,” Dr. Childs says. Second, if a virtual colonoscopy shows an abnormal finding, a follow-up regular colonoscopy would be needed.

Researchers are investigating the optimal role for virtual colonoscopy in colorectal cancer screening, Dr. Kumar notes. “In the future, virtual colonoscopy may have more utility, but it will always go hand-in-hand with regular colonoscopy,” he adds.

Flexible sigmoidoscopy. In this procedure, a sigmoidoscope, which is similar to a colonoscope, is inserted through the anus toward the colon and rectum. Like a colonoscopy, a sigmoidoscopy provides detailed interior images of the rectal area.

Because the sigmoidoscope is only about 2 feet long – compared with 4 to 6 feet for a colonoscope – sigmoidoscopy is not as invasive and potentially less uncomfortable than a colonoscopy. Due to its shorter length, however, the sigmoidoscope provides a view of only a portion of the colon; suspicious lesions elsewhere along the length of the colon cannot be seen. And if sigmoidoscopy results are suspicious, a colonoscopy is needed, Dr. Kumar says.

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