Fecal DNA Testing: Passing Fancy or the Demise of Colonoscopy?
For many years, there have been attempts to find easier and less expensive alternatives to colonoscopy as a means to screen for colorectal cancer. The stakes are quite high. There were an estimated 136,830 new cases of colorectal cancer in the United States in 2014, and 50,310 deaths from colorectal cancer in the same period. The estimated 5 year survival is approximately 64.7%
As alarming as these statistics are, there has been a clear trend toward improvement since the advent of routine screening colonoscopy. Medicare began to pay for screening colonoscopies in “high risk” individuals in the 1980's and 1990’s and began coverage for average risk people in 2001. Most analysts attribute the steady decrease in the rate of new cases and deaths from colorectal cancer to the more widespread acceptance of screening colonoscopy. In fact, it is estimated that if everyone age 50 (the recommended started point for most patients)and up were screened via colonoscopy, it would result in an 80% prevention of colon cancer, and a 60% reduction in deaths from colon cancer.
Despite these compelling facts, it is estimated that at least one in three Americans of the appropriate age(50-75)has not been tested for colorectal cancer, and therefore is needlessly at risk for this preventable problem. The reasons for this are multiple, and include inadequate public awareness, cost, inadequate access to medical resources, and fear of what some perceive to be an invasive medical procedure.
Current guidelines indicate that colonoscopy is the superior method for screening, since it effective for both early detection of colorectal cancer, as well as prevention(by detecting and removing pre-cancerous polyps). Average risk individuals are advised to have colonoscopy starting at age 50(45 for African Americans), then every 10 years if normal. For individuals who decline colonoscopy, yearly FIT(fecal immunochemical testing) is advised as an alternative. This is a test that can detect tiny amounts of blood in the stool, which may indicate the presence of a colon tumor. While FIT is less invasive than colonoscopy(it involves submitting a scraping from a stool specimen), it is problematic in the sense that it is less likely to pick up cancers than colonoscopy, only detecting 79% of cancers.
To try and combat this lower rate of detection, researchers have combined the FIT test with a fecal DNA test, which can detect abnormal DNA in the stool, which has been shed by tumor cells in the colon. The results were encouraging. The DNA test discovered 60 of the 65 cancers for an accuracy rate of approximately 92%. The cost, according to Cologuard, by Exact Sciences Laboratories, is $599.
The role for fecal DNA testing remains to be seen. Like FIT, it is less likely to find colon cancers than colonoscopy. If it is utilized routinely to screen individuals, other issues such as the high false positive rate(meaning an abnormal stool test, when there is actually no tumor present), as well as the frequency with which such tests should be done, must be resolved.
Where does fecal DNA and FIT “fit” into my practice?(sorry-couldn’t help it!). I continue to recommend colonoscopy as the screening test of choice. It is hard for me to offer other tests as “first line”. Colonoscopy is the “gold standard” for accuracy, is well documented to save lives, and has withstood the test of time as en effective tool for detecting, and preventing colon cancer.
I offer fecal DNA testing and/or FIT as an alternate strategy for patients who refuse to undergo colonoscopy, or who-because of other serious medical conditions-may be poor candidates for colonoscopy. While cost and accuracy with fecal DNA testing remain a problem, it definitely represents an advance by offering another tool in the fight against colon cancer.