Asad Umar, DVM, PhD, Chief of the Gastrointestinal and Other Cancers Research Group at the National Cancer Institute, shared developments in colorectal cancer screening methods with NIH MedlinePlus magazine.
What should patients know to help determine the best colon cancer screening test for them?
Colonoscopy is considered the gold standard. It is effective for screening and detection, and it is therapeutic as well since adenomas (a type of precancerous polyp) that are found during colonoscopy can be removed. That’s the biggest advantage of colonoscopy as opposed to all other techniques. Another advantage is it is needed only once every 10 years if results are negative.
Other less invasive tests include flexible sigmoidoscopy. It is less invasive and takes less time than colonoscopy. In NCI’s study called the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, flexible sigmoidoscopy was found to be reasonable in detection of adenomas, and acceptance of screening flexible sigmoidoscopy was high among participants.
The fecal occult blood test—FOBT—is one of the older screening methods. It looks for blood in the feces, which can indicate polyps or tumors. A newer version called the fecal immunochemical test—FIT—looks for only human blood, so there is no need for dietary restrictions such as not eating meat before the test. FIT or FOBT are recommended annually.
Are there other screening methods?
A couple of new tests approved recently by the FDA are called Cologuard® and ColoVantage®. Cologaurd is a DNA panel combined with FIT. A stool sample is collected and examined for genetic mutations that indicate possible cancers or adenomas. ColoVantage, on the other hand, is a bloodbased test that detects circulating DNA from adenomas and colorectal cancers. It is offered to individuals who refuse or are non-adherent to other testing options.
CT colonography, also known as virtual colonoscopy, uses X-ray technology to look for polyps. It is less invasive than colonoscopy but you still have to go through the same prep, and most people really dislike that prep. That’s where the issues are in the general population, not getting enough people to go for a colonoscopy.
Are there genetic markers that might help identify those who could benefit from being tested earlier than generally recommended?
Colonoscopy is recommended at age 50 for the general population. But for African Americans it is recommended starting at age 45 and for Alaska Natives at age 40. They are reported to have more adenomas as well as colorectal cancer, and mortality is higher in both groups.
In terms of family history, other than familial cancer syndromes including hereditary non-polyposis colorectal cancer (HNPCC or Lynch syndrome) and familial adenomatous polyposis (FAP), there are no clear-cut recommendations and no genetic marker has been identified. But it would not hurt for people with a family history to get tested at age 45.