Ketan Kulkarni, MD

Testing for colorectal cancer without the colonoscopy

By: Ketan Kulkarni, MD

A new noninvasive test to detect colon and rectal cancer is offering hope that more people will be willing to be screened, driving down the rates of these cancers. Cologuard is the first stool DNA colorectal cancer screening test to be approved by the Food and Drug Administration.

The test is a potentially exciting advancement that could one day change the way we screen for colorectal cancer—but not yet. Many questions remain about the optimal use of stool-based testing, which detects the presence of red blood cells and DNA mutations that may be indicative of cancer.

In the trial upon which the FDA based its approval,  Cologuard was very sensitive for the detection of cancer, but it found less than half of all advanced adenomas (precancerous polyps) and even a smaller percentage of regular adenomas. People who have a positive result are advised to have a colonoscopy.

Additional limitations of stool-based DNA testing include the fairly high false positive rate, the complexity of the test itself, the lack of well-defined screening intervals, and the greater cost when compared to current stool immunochemical tests.

Colorectal cancer is the third most common cancer and the second leading cause of cancer-related deaths in the United States among cancers that affect men and women, according to the Centers for Disease Control and Prevention.

The CDC estimates that at least 60 percent of colorectal cancer deaths could be prevented if everyone age 50 or older had the recommended screenings—fecal occult blood test, sigmoidoscopy, or colonoscopy.

The gold standard for colorectal cancer screening is still colonoscopy, in which your doctor uses a flexible tube to examine the inside of your colon. It’s been successful at lowering cancer deaths by not only detecting cancer at earlier stages, but by also detecting precancerous polyps. Your doctor can remove these polyps during the colonoscopy and prevent cancer.

Current guidelines call for testing to start at age 50 in those individuals without a family history, but about half of all eligible people haven’t been properly screened with one of the recommended tools.

The approval of Cologuard holds much promise as a screening option that is noninvasive, can produce reliable results and provide a better patient experience. However we’ll need more data to determine how accurate Cologuard will be in the “real world”, outside the context of a clinical trial, before it becomes standard practice.